Hainan Meteorological Service

A suite of climate change indices derived from daily temperature and precipitation data, with a primary focus on extreme events, were computed and analyzed. By setting an exact formula for each index and using specially designed software, analyses done in different countries have been combined seamlessly. This has enabled the presentation of the most up‐to‐date and comprehensive global picture of trends in extreme temperature and precipitation indices using results from a number of workshops held in data‐sparse regions and high‐quality station data supplied by numerous scientists world wide. Seasonal and annual indices for the period 1951–2003 were gridded. Trends in the gridded fields were computed and tested for statistical significance. Results showed widespread significant changes in temperature extremes associated with warming, especially for those indices derived from daily minimum temperature. Over 70% of the global land area sampled showed a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights. Some regions experienced a more than doubling of these indices. This implies a positive shift in the distribution of daily minimum temperature throughout the globe. Daily maximum temperature indices showed similar changes but with smaller magnitudes. Precipitation changes showed a widespread and significant increase, but the changes are much less spatially coherent compared with temperature change. Probability distributions of indices derived from approximately 200 temperature and 600 precipitation stations, with near‐complete data for 1901–2003 and covering a very large region of the Northern Hemisphere midlatitudes (and parts of Australia for precipitation) were analyzed for the periods 1901–1950, 1951–1978 and 1979–2003. Results indicate a significant warming throughout the 20th century. Differences in temperature indices distributions are particularly pronounced between the most recent two periods and for those indices related to minimum temperature. An analysis of those indices for which seasonal time series are available shows that these changes occur for all seasons although they are generally least pronounced for September to November. Precipitation indices show a tendency toward wetter conditions throughout the 20th century.

A climate change workshop for the Middle East brought together scientists and data for the region to produce the first area‐wide analysis of climate extremes for the region. This paper reports trends in extreme precipitation and temperature indices that were computed during the workshop and additional indices data that became available after the workshop. Trends in these indices were examined for 1950–2003 at 52 stations covering 15 countries, including Armenia, Azerbaijan, Bahrain, Cyprus, Georgia, Iran, Iraq, Israel, Jordan, Kuwait, Oman, Qatar, Saudi Arabia, Syria, and Turkey. Results indicate that there have been statistically significant, spatially coherent trends in temperature indices that are related to temperature increases in the region. Significant, increasing trends have been found in the annual maximum of daily maximum and minimum temperature, the annual minimum of daily maximum and minimum temperature, the number of summer nights, and the number of days where daily temperature has exceeded its 90th percentile. Significant negative trends have been found in the number of days when daily temperature is below its 10th percentile and daily temperature range. Trends in precipitation indices, including the number of days with precipitation, the average precipitation intensity, and maximum daily precipitation events, are weak in general and do not show spatial coherence. The workshop attendees have generously made the indices data available for the international research community.

Abstract A data assimilation scheme has been coupled to the Canadian Middle Atmosphere Model, providing, for the first time, the capability of assimilating data from the ground to the top of the mesosphere (about 95 km). This model is a full general circulation model with on‐line fully interactive chemistry involving 127 gas‐phase and heterogeneous reactions. Thus, feedback between dynamics, chemistry and radiation occurs in every model time step. In this work, validation of the system for tropospheric and lower stratospheric analyses is undertaken with the standard observation set used in operational weather forecasting. Results are found to agree reasonably well with radiosonde observations and with Met Office (UK) analyses. Although ozone is not assimilated, ozone fields match total column observations well in terms of synoptic patterns. However, due to model biases, total column values are too large at mid‐latitudes and too small in the tropics. Since the assimilation scheme was designed for tropospheric weather prediction, its application to a middle atmosphere model can help to identify the challenges of assimilating data from this region of the atmosphere.

Using accurate inputs of wind speed is crucial in wind resource assessment, as predicted power is proportional to the wind speed cubed. This study outlines a methodology for combining multiple ocean satellite winds and winds from WRF simulations in order to acquire the accurate reconstructed offshore winds which can be used for offshore wind resource assessment. First, wind speeds retrieved from Synthetic Aperture Radar (SAR) and Scatterometer ASCAT images were validated against in situ measurements from seven coastal meteorological stations in South China Sea (SCS). The wind roses from the Navy Operational Global Atmospheric Prediction System (NOGAPS) and ASCAT agree well with these observations from the corresponding in situ measurements. The statistical results comparing in situ wind speed and SAR-based (ASCAT-based) wind speed for the whole co-located samples show a standard deviation (SD) of 2.09 m/s (1.83 m/s) and correlation coefficient of R 0.75 (0.80). When the offshore winds (i.e., winds directed from land to sea) are excluded, the comparison results for wind speeds show an improvement of SD and R, indicating that the satellite data are more credible over the open ocean. Meanwhile, the validation of satellite winds against the same co-located mast observations shows a satisfactory level of accuracy which was similar for SAR and ASCAT winds. These satellite winds are then assimilated into the Weather Research and Forecasting (WRF) Model by WRF Data Assimilation (WRFDA) system. Finally, the wind resource statistics at 100 m height based on the reconstructed winds have been achieved over the study area, which fully combines the offshore wind information from multiple satellite data and numerical model. The findings presented here may be useful in future wind resource assessment based on satellite data.

Abstract Total and extreme precipitation in Hainan Island was investigated in this study, based on consistent meteorological data for the period 1962–2005. Results show that tropical cyclones mainly impact Hainan Island between June and November, during which time they account for more than one‐third of the total precipitation. Over the past four decades, the number of TCs impacting Hainan Island has significantly decreased. Correspondingly, the TC precipitation and its contribution to the total precipitation have slightly reduced. Extreme rainfall events because of cyclones are responsible for nearly 60% of Hainan's overall ‘daily extreme precipitation’ and 23% of Hainan's total precipitation. Noticeably, the number of extreme heavy precipitation days and total amount of precipitation from those extreme events influenced by TCs has increased. On average, the precipitation amount and the number of days of extreme events caused by each cyclone have been significantly increased. Copyright © 2007 Royal Meteorological Society

Abstract. Aerosol hygroscopicity strongly influences the number size distribution, phase state, optical properties, and multiphase chemistry of aerosol particles. Due to the large number of organic species in atmospheric aerosols, the determination of the hygroscopicity of ambient aerosols remains challenging. In this study, we measured the hygroscopic properties of 23 organics, including carboxylic acids, amino acids, sugars, and alcohols, using a hygroscopicity tandem differential mobility analyzer (HTDMA). Earlier studies have characterized the hygroscopicity either for a limited number of organic compounds using similar techniques or for particles at sizes beyond the microscale range or even bulk samples using other methodologies. Here, we validate these studies and extend the data by measuring the hygroscopicity of a broader suite of organics for particles with sizes under the submicrometer range that are more atmospherically relevant. Moreover, we systematically evaluate the roles of that related physicochemical properties play in organic hygroscopicity. We show that the hygroscopicity of organics varies widely with functional groups and organics with the same carbon number but that more functional groups show higher hygroscopicity. However, some isomers that are very similar in molecular structure show quite different hygroscopicity, demonstrating that other physicochemical properties, such as water solubility, may contribute to their hygroscopicity as well. If the organics are fully dissolved in water (solubility >7×10-1 g mL−1), we found that their hygroscopicity is mainly controlled by their molecular weight. For the organics that are not fully dissolved in water (slightly soluble: 5×10-4 g mL−1 < solubility < 7×10-1 g mL−1), we observed that some of them show no obvious water uptake, which is probably due to the fact that they may not deliquesce under our studied conditions up to 90 % relative humidity (RH). The other type of slightly soluble organic material is moderately hygroscopic, and the larger its solubility is, the higher its hygroscopicity will be. Moreover, the hygroscopicity of organics generally increased with O:C ratios, although this relationship is not linear.

Field measurements of reactive halogen and sulfur gas emissions were performed at the world's largest salt pan, the Salar de Uyuni, Southern Altiplano, Bolivia (19.8°–20.7°S, 67.0°–68.2°W), during the dry season in October/November 2002. Bromine monoxide (BrO) and sulfur dioxide (SO 2 ) were studied by ground‐based scattered light Multi Axis Differential Optical Absorption Spectroscopy (MAX‐DOAS) at various locations upwind and inside the salar. Significant amounts of BrO were found at all locations with the lowest levels at the northern edge of the salar (upwind), while BrO slant column densities (differential with respect to zenith) of up to 3.7 × 10 14 molec/cm 2 were observed inside the salar. Using the MAX‐DOAS vertical profile information BrO mixing ratios of >20 ppt are calculated, which can have significant impact on tropospheric ozone chemistry both locally and regionally. SO 2 slant column densities of >5 × 10 16 molec/cm 2 were found around the salar, suggesting emissions from volcanic activity.

Based on the satellite data from the Climate Prediction Center morphing (CMORPH) at very high spatial and temporal resolution, the effects of urbanization on precipitation were assessed over the Pearl River Delta (PRD) metropolitan regions of China. CMORPH data well estimates the precipitation features over the PRD. Compared to the surrounding rural areas, the PRD urban areas experience fewer and shorter precipitation events with a lower precipitation frequency (ratio of rainy hours, about 3 days per year less); however, short-duration heavy rain events play a more significant role over the PRD urban areas. Afternoon precipitation is much more pronounced over the PRD urban areas than the surrounding rural areas, which is probably because of the increase in short-duration heavy rain over urban areas.

An improved fuzzy c-means algorithm is put forward and applied to deal with meteorological data on top of the traditional fuzzy c-means algorithm. The proposed algorithm improves the classical fuzzy c-means algorithm (FCM) by adopting a novel strategy for selecting the initial cluster centers, to solve the problem that the traditional fuzzy c-means (FCM) clustering algorithm has difficulty in selecting the initial cluster centers. Furthermore, this paper introduces the features and the mining process of the open source data mining platform WEKA, while it doesn't implement the FCM algorithm. Considering this shortcoming of WEKA, we successfully implement the FCM algorithm and the advanced FCM algorithm taking advantage of the basic classes in WEKA. Finally, the experimental clustering results of meteorological data are given, which can exactly prove that our proposed algorithm will generate better clustering results than those of the K-Means algorithm and the traditional FCM algorithm.

Abstract. Brown carbon (BrC) is a special type of organic aerosol (OA), capable of absorbing solar radiation from near-ultraviolet (UV) to visible wavelengths, which may lead to an increased aerosol radiative effect in the atmosphere. While high concentrations of OAs have been observed in the Pearl River Delta (PRD) region of China, the optical properties and corresponding radiative forcing of BrC in the PRD are still not well understood. In this work, we conducted a set of comprehensive measurements of atmospheric particulate matter from 29 November 2014 to 2 January 2015 to investigate aerosol compositions, optical properties, source origins, and radiative forcing effects at a suburban station in Guangzhou. The particle absorption Ångström exponent (AAE) was deduced and utilized to distinguish light absorption by BrC from that by black carbon (BC). The results showed that the average absorption contributions of BrC were 34.1±8.0 % at 370 nm, 23.7±7.3 % at 470 nm, 16.0±6.7 % at 520 nm, 13.0±5.4 % at 590 nm, and 8.7±4.3 % at 660 nm. A sensitivity analysis of the evaluation of the absorption Ångström exponent of BC (AAEBC) was conducted based on the Mie theory calculation assuming that the BC-containing aerosol was mixed with the core–shell and external configurations. The corresponding uncertainty in AAEBC was acquired. We found that variations in the imaginary refractive index (RI) of the BC core can significantly affect the estimation of AAEBC. However, AAEBC was relatively less sensitive to the real part of the RI of the BC core and was least sensitive to the real part of the RI of the non-light-absorbing shell. BrC absorption was closely related to aerosol potassium cation content (K+), a common tracer of biomass burning emissions, which was most likely associated with straw burning in the rural area of the western PRD. Diurnal variation in BrC absorption revealed that primary organic aerosols had a larger BrC absorption capacity than secondary organic aerosols (SOAs). Radiative transfer simulations showed that BrC absorption may cause 2.3±1.8 W m−2 radiative forcing at the top of the atmosphere (TOA) and contribute to 15.8±4.4 % of the aerosol warming effect. A chart was constructed to conveniently assess the BrC radiative forcing efficiency in the studied area with reference to certain aerosol single-scattering albedo (SSA) and BrC absorption contributions at various wavelengths. Evidently, the BrC radiative forcing efficiency was higher at shorter wavelengths.

South China experienced a series of unprecedented extreme heat wave (EHW) events in early summer (June–July) 2020, which broke the historical record for the frequency of EHW events since 1979. Observational analyses showed that the prolonged EHW events were primarily induced by an anomalous tropospheric circulation over South China with a barotropic structure. This was attributed to the exceptional westward displacement of the western Pacific subtropical high (WPSH) and the eastward-extended upper-level South Asia high (SAH). In addition, the value of the SAH–WPSH index, which describes the relative displacement of the SAH and WPSH, also broke the historical record. Further analysis revealed that the EHW events in South China were closely associated with warming of the tropical Indian Ocean (TIO) sea surface temperature (SST), which affected both the SAH and WPSH via atmospheric teleconnections. Sensitivity and pacemaker experiments using an atmosphere-only and a coupled global climate model, respectively, suggested that the anomalous warming of the SST in the TIO directly caused the significant southeastward displacement of the intensified SAH as a result of diabatic heating in the troposphere. This heating also led to a westward-displaced WPSH via an induced mid- to lower tropospheric Kelvin wave and the associated Ekman divergence. In summary, warming in the TIO sustained exceptional shifts in both the SAH and WPSH, which favored the formation of a stationary anomalous high over South China that ultimately contributed to the record-breaking EHW events in early summer 2020.

During the solar eclipse of August 11, 1999, intensive measurements of UV solar irradiance and total ozone were performed at a number of observatories located near the path of the Moon's shadow. At the Laboratory of Atmospheric Physics (LAP) of the Aristotle University of Thessaloniki, Greece, global and direct spectra of UV solar irradiances (285–365 nm) were recorded with a double monochromator, and erythemal irradiances were measured with broadband pyranometers. In addition, higher‐frequency measurements of global and direct irradiances at six UV wavelengths were performed with a single Brewer spectrophotometer. Total ozone measurements were also performed with Dobson and Brewer spectrophotometers at Hradec Kralove (Czech Republic), Ispra (Italy), Sestola (Italy), Hohenpeissenberg (Germany), Bucharest (Romania), Arosa (Switzerland), and Thessaloniki (Greece). From the spectral UV measurements the limb darkening effect of the solar disk was tentatively quantified from differences of measured solar spectral irradiances at the peak of the eclipse (near to limb conditions) and before the eclipse. Two blackbody curves were fit to the preeclipse and peak eclipse spectra, which have shown a difference in effective temperatures of about 165°K between the limb and the whole of the solar disk. The limb darkening effect is larger at the shorter UV wavelengths. The ratio of the diffuse to direct solar irradiances during the eclipse shows that the diffuse component is reduced much less compared to the decline of the direct solar irradiance at the shorter wavelengths. Moreover, a 20‐min oscillation of erythemal UV‐B solar irradiance was observed before and after the time of the eclipse maximum under clear skies, indicating a possible 20‐min fluctuation in total ozone, presumably caused by the eclipse‐induced gravity waves. This work also shows that routine total ozone measurements with a Brewer or a Dobson spectrophotometer should be used with caution during a solar eclipse. This is because the diffuse light increases by more than 30% with respect to the direct solar radiation, increasing more at the shorter wavelength side of the UV spectrum. This plausible mechanism introduces an artificial decrease in total ozone during solar eclipse of more than 30 Dobson units (DU), which is confirmed by all Brewer and Dobson measurements. Changes in total ozone cited earlier in the refereed literature have not been confirmed in the present study.

The hydrological cycle has significant effects on the terrestrial carbon (C) balance through its controls on photosynthesis and C decomposition. A detailed representation of the water cycle in terrestrial C cycle models is essential for reliable estimates of C budgets. However, it is challenging to accurately describe the spatial and temporal variations of soil water, especially for regional and global applications. Vertical and horizontal movements of soil water should be included. To constrain the hydrology-related uncertainty in modelling the regional C balance, a three-dimensional hydrological module was incorporated into the Integrated Terrestrial Ecosystem Carbon-budget model (InTEC V3.0).We also added an explicit parameterization of wetlands. The inclusion of the hydrological module considerably improved the model’s ability to simulate C content and balances in different ecosystems. Compared with measurements at five flux-tower sites, the model captured 85% and 82% of the variations in volumetric soil moisture content in the 0–10 cm and 10– 30cmdepths during the growing season and84%of the interannual variability in the measuredCbalance. The simulations showed that lateral subsurface water redistribution is a necessary mechanism for simulating water table depth for both poorly drained forest and peatland sites. Nationally, soil C content and their spatial variability are significantly related to drainage class. Poorly drained areas are important C sinks at the regional scale, however, their soil C content and balances are difficult to model and may have been inadequately represented in previous C cycle models. The InTEC V3.0 model predicted an annual net C uptake by Canada’s forests and wetlands for the period 1901–1998 of 111.9 Tg C yr-1, which is 41.4 Tg C yr-1 larger than our previous estimate (InTEC V2.0). The increase in the net C uptake occurred mainly in poorly drained regions and resulted from the inclusion of a separate wetland parameterization and a detailed hydrologic module with lateral flow in InTEC V3.0.

Radar and satellite joint observation data can provide a more efficient way to study landfalling typhoon precipitation, but rarely does this combination of circumstances occur. In this study, we attempt to reveal the precipitation characteristics of typhoon Lekima (2019) at landfall by using joint observations from GPM satellite and S-band Doppler radar. The results suggest that the precipitation microphysical mechanisms are different among typhoon eyewall (EW), inner rainband (IR), and outer rainband (OR) during landfall. Beneath melting layer, collision-coalescence process dominates the precipitation in EW region, with large‐/mid- size raindrops (~1.6 mm) as the main components of precipitation. Collision-coalescence, breakup, and evaporation processes are in near balance within the precipitation of IR region, leading to prevailing mid‐/small- size raindrops (~1.3 mm) of this region. Melting and evaporation processes are the main precipitation microphysical mechanism in OR region and a small amount of large-size drops (~1.7 mm) constitute the majority of precipitation. Moreover, the large values of radar spectrum width exhibit an appreciable correlation with satellite detected effective reflectivity (Ze) center, mass-weighted mean diameter (Dm) center, and storm top height (STH) peak, jointly indicating the strong convection activity inside landfalling typhoon Lekima, which further enlightens us to make better use of joint observation data from Doppler weather radar and GPM satellite to analyze the microphysics and dynamics associated with heavy rainfall during typhoon landfall in operational applications.

Abstract This study documents the detailed features and processes of convection initiation (CI) at a coastal rainfall hotspot in South China, with emphasis on the typical meteorological conditions and effects of small‐scale orography. The CI occurrences are identified using high‐quality radar mosaics during 7‐year warm seasons. They tend to maximize in low‐lying areas adjacent to coastal small‐scale mountains rather than on the windward slopes of major mountains as previously expected. The genesis of the coastal convection exhibits a remarkable diurnal peak in the early afternoon and mostly occurs on the days of low‐level southwesterlies with a jet‐nose structure in offshore region. These onshore flows enhance the low‐level moistening and convergence on coasts. The characteristic synoptic patterns become common after the onset of summer monsoon, suggesting the key role of monsoonal flows in triggering coastal convection. Driven by the atmospheric conditions of the dominant synoptic pattern, quasi‐idealized numerical simulations demonstrate that the coastal small‐scale mountains disturb the low‐level onshore flow and produce multiple enhanced convergent zones downstream of the mountains. The induced local variations in upward motion and moisture pooling explain the CI occurrences that are located close to these small‐scale mountains. When these mountains are artificially removed in the simulation, convection preferentially initiates on the windward slopes of major mountains as expected. The findings suggest that the small‐scale orography can strongly regulate the local patterns of CI hotspot through disturbing low‐level onshore flow. An explicit resolving of the small‐scale coastal orography is warranted to improve the modeling of local severe weather.

Near-surface wind data are particularly important for Hainan Island and the South China Sea, and there is a wide range of wind data sources. A detailed understanding of the reliability of these datasets can help us to carry out related research. In this study, the hourly near-surface wind data from the High-Resolution China Meteorological Administration (CMA) Land Data Assimilation System (HRCLDAS) and the fifth-generation ECMWF atmospheric reanalysis data (ERA5) were evaluated by comparison with the ground automatic meteorological observation data for Hainan Island and the South China Sea. The results are as follows: (1) the HRCLDAS and ERA5 near-surface wind data trend was basically the same as the observation data trend, but there was a smaller bias, smaller root-mean-square errors, and higher correlation coefficients between the near-surface wind data from HRCLDAS and the observations; (2) the quality of HRCLDAS and ERA5 near-surface wind data was better over the islands of the South China Sea than over Hainan Island land. However, over the coastal areas of Hainan Island and island stations near Sansha, the quality of the HRCLDAS near-surface wind data was better than that of ERA5; (3) the quality of HRCLDAS near-surface wind data was better than that of ERA5 over different types of landforms. The deviation of ERA5 and HRCLDAS wind speed was the largest along the coast, and the quality of the ERA5 wind direction data was poorest over the mountains, whereas that of HRCLDAS was poorest over hilly areas; (4) the accuracy of HRCLDAS at all wind levels was higher than that of ERA5. ERA5 significantly overestimated low-grade winds and underestimated high-grade winds. The accuracy of HRCLDAS wind ratings over the islands of the South China Sea was significantly higher than that over Hainan Island land, especially for the higher wind ratings; and (5) in the typhoon process, the simulation of wind by HRCLDAS was closer to the observations, and its simulation of higher wind speeds was more accurate than the ERA5 simulations.

A Pacific–Japan (PJ) pattern index is defined based on the singular value decomposition (SVD) analysis of summertime 500-hPa height in East Asia and precipitation in the tropical western North Pacific (WNP). The time series of this PJ index shows clearly the interannual and interdecadal variations since 1948. Idealized atmospheric general circulation model (AGCM) experiments were carried out to understand the remote and local SST forcing in causing the interannual variations of the PJ pattern and interdecadal variations of the PJ-like pattern. It is found that the PJ interannual variation is closely related to El Niño–Southern Oscillation (ENSO). A basinwide warming occurs in the tropical Indian Ocean (TIO) during El Niño mature winter. The TIO warming persists from the El Niño peak winter to the succeeding summer. Meanwhile, a cold SST anomaly (SSTA) appears in the eastern WNP and persists from the El Niño mature winter to the succeeding summer. Idealized AGCM experiments that separate the TIO and WNP SSTA forcing effects show that both the remote eastern TIO forcing and local WNP SSTA forcing are important in affecting atmospheric heating anomaly in the WNP monsoon region, which further impacts the PJ interannual teleconnection pattern over East Asia. In contrast to the interannual variation, the interdecadal change of the PJ-like pattern is primarily affected by the interdecadal change of SST in the TIO rather than by the local SSTA in the WNP.

A data-driven impact-time-control guidance (DD-ITCG) method based on proportional navigation guidance (PNG) is presented in this study, in which the assumption of constant velocity adopted in previous reports is not necessary, and it is applicable to cases with significant velocity changes. The motivation of the presented DD-ITCG is that, for a given flight state vector (FSV, including position and velocity) and a given target position, the PNG trajectory from this FSV to this target as well as the corresponding PNG time-to-go (TGO) are determined. Based on this fact, a database including input FSV and output of PNG TGO is built. At a time instant in DD-ITCG, there are two TGO quantities, one is PNG TGO of PNG trajectory, and the other one is the required TGO. Hence there is a TGO error between PNG TGO and required TGO. Then a TGO error rate with opposite sign of TGO error is set to decrease the TGO error to zero. The relation between the TGO error rate and the DD-ITCG commands is analyzed, based on which the DD-ITCG commands are computed by virtue of the database. Case studies of a hypersonic flight vehicle impact time control show the performances of the presented DD-ITCG method, and some observations in these case studies are discussed.

In order to examine the temporal variation of the atmospheric CO2 concentration in a temperate deciduous forest, and its relationship with meteorological conditions, continuous measurements of CO2 and meteorological parameters have been made since 1993 on a tower at Takayama in the central part of Japan. In addition to an average secular increase in atmospheric CO2 of 1.8 ppm yr−1, diurnal variation with a maximum during the night-time to early morning and a minimum in the afternoon is observed from late spring to early fall; the diurnal cycle is not so clearly observed in the remaining seasons of the year. A concentration difference between above and below the canopy, and its diurnal variation, can also be seen clearly in summer. Daily mean concentration data show a prominent seasonal cycle. The maximum and the minimum of the seasonal cycle occur in April and from mid August to mid September, respectively. Day-to-day changes in the diurnal cycle of CO2 are highly dependent on the day-to-day variations in meteorological conditions. However, CO2 variations on longer time scales (>10 d) appear to be linearly related to changes in respiration. At Takayama, variations in the 10-d standard deviation of daily mean CO2 data and 10-d averaged respiration show distinct relationships with soil temperature during spring and fall seasons. In spring, respiration has a stronger exponential dependence on soil temperature than in fall. Interestingly, in summer when soil temperature becomes greater than about 15 °C, biological respiration becomes more variable and independent of the soil temperature. Thus, at the Takayama site, the Q10 relationship is seasonally dependent, and does not represent well the biological respiration process when the soil temperature rises above 15 °C.

Abstract Seawater quality degradation is caused by diverse, non-linearly interacting factors, knowledge of which is essential for understanding and predicting water quality trends. Currently, most water-quality research has been based on certain assumptions to employ linear approaches for solving simplified problems, such as numerical simulations or cumulative impact assessments. To improve the accuracy and ease of prediction, the random forest method has been increasingly employed as a good alternative to traditional prediction methods. In the present study, the random forest method was adopted to construct a model of the water quality response of Xincun Lagoon to anthropogenic nutrient inputs based on a limited amount of sample data, aiming to (a) identify the critical sources of nutrient inputs that affect the meeting of water quality objectives so as to minimize the socioeconomic impact on secondary stakeholders; and (b) predict the impact of a reduction of anthropogenic nutrient inputs on water quality improvement. It can be seen from the results that the intensity of stressors generated by different human activities presents an obvious non-linear superposition pattern, and the random forest method is one of the feasible solutions to this phenomenon; in addition, the impact on the lagoon ecosystem is not directly related to the intensity of the pressure source, for example, coastal aquaculture is more important than shallow sea cage aquaculture. Therefore, the method established in this paper can be used to identify the key pressure sources during the restoration of the lagoon environment, so as to achieve the unity of economy and effectiveness.