Decreasing Trend In Precipitation Research Articles

Understanding future hydrologic challenges: Modelling the impact of climate change on river runoff in central Italy

Central Italy’s diverse ecosystems and landscapes are susceptible to the Mediterranean climate change, affecting water resources and riverine systems. Managing these resources is crucial for the nation’s sustainable development and resilience. This research assesses potential long-term climate change impacts on river runoff in central Italy’s highly regulated Aterno-Pescara River watershed. We simulated current and future river runoff using the Soil and Water Assessment Tool (SWAT+). Climate projections from 5 Global Climate Models (GCMs) under two emissions scenarios are used to quantify potential runoff and drought characteristic changes in SWAT+ to investigate future (2015 – 2100) climate change impacts on river runoff. All GCMs predicted increasing daily temperature (up to 0.6 °C decade−1 at 95 % confidence level) and decreasing precipitation trends (−16.4 mm decade−1), resulting in negative river runoff trends (−0.036 m3s−1 decade−1). Uncertainties exist regarding variable magnitudes among GCMs and scenarios. Analyzing 12-month standardized precipitation and runoff drought indices using projections data revealed a strong correlation between drought indices (Pearson correlation coefficient ranges between 0.63 − 0.93 among GCMs). The run-sum technique for both indices showed potential frequent, severe, and prolonged future droughts, with meteorological droughts possibly lasting up to 105 months (severity 163) and hydrological droughts exceeding 100 months (severity over 150). This study provides crucial insights for central Italy’s policymakers, emphasizing the need for strategies addressing climate change impacts on water resources for future sustainability.

Glacier Mass Balance and Its Impact on Land Water Storage in the Southeastern Tibetan Plateau Revealed by ICESat-2 and GRACE-FO

The southeastern Tibetan Plateau (SETP), which hosts the most extensive marine glaciers on the Tibetan Plateau (TP), exhibits enhanced sensitivity to climatic fluctuations. Under global warming, persistent glacier mass depletion within the SETP poses a risk to water resource security and sustainability in adjacent nations and regions. This study deployed a high-precision ICESat-2 satellite altimetry technique to evaluate SETP glacier thickness changes from 2018 to 2022. Our results show that the average change rate in glacier thickness in the SETP is −0.91 ± 0.18 m/yr, and the corresponding glacier mass change is −7.61 ± 1.52 Gt/yr. In the SETP, the glacier mass loss obtained via ICESat-2 data is larger than the mass change in total land water storage observed by the Gravity Recovery and Climate Experiment follow-on satellite (GRACE-FO), −5.13 ± 2.55 Gt/yr, which underscores the changes occurring in other land water components, including snow (−0.44 ± 0.09 Gt/yr), lakes (−0.06 ± 0.02 Gt/yr), soil moisture (1.88 ± 1.83 Gt/yr), and groundwater (1.45 ± 0.70 Gt/yr), with a closure error of −0.35 Gt/yr. This demonstrates that this dramatic glacier mass loss is the main reason for the decrease in total land water storage in the SETP. Generally, there are decreasing trends in solid water storage (glacier and snow) against stable or increasing trends in liquid water storage (lakes, soil moisture, and groundwater) in the SETP. This persistent decrease in solid water is linked to the enhanced melting induced by rising temperatures. Given the decreasing trend in summer precipitation, the surge in liquid water in the SETP should be principally ascribed to the increased melting of solid water.

Contrasting latitudinal evolution of East Asian monsoonal precipitation during the Last Interglacial (130–120 ka)

Evolution of East Asian monsoonal precipitation across the Last Interglacial (LIG) remains controversial, owing to the discrepancies between various proxies and their low temporal resolution. Through a transient high-resolution global climate simulation covering the interval of 130–120 ka, we illustrate a long-term increasing (decreasing) trend in summer precipitation over south China (northeast Asia) during the LIG (i.e. 130–120 ka). The out-of-phase precipitation evolution across latitudes were coherently regulated by the weakened monsoonal circulation, southward moved western North Pacific high, and southward displaced East Asian westerly jet from the early to late LIG. These atmospheric circulation variations were in turn determined by sea surface temperature anomalies over the Pacific and the propagation of extratropical Rossby waves originating from North Africa. Our results may provide important insights for reconciling discrepancies between precipitation proxies during the LIG and for precipitation behavior in a warmer-than-present world.

Recent Precipitation Trends in Six Districts of the Ken River Basin of Bundelkhand Region, India

The future development and sustainable management of water resources will be greatly influenced by the trend analysis of precipitation. This paper focuses on the analysis of rainfall trends in the Bundelkhand region, particularly in six districts covering the Ken basin. Mann-Kendall test was employed to identify potential trends, and the Sen’s slope estimator was utilized to quantify the magnitude of change during 1990 to 2020. Given that a significant portion of rainfall occurs during the southwest monsoon season, the study included both seasonal (monsoon) and annual analyses. The findings indicated a decreasing trend in precipitation for both the monsoon season and the annual scale, although many districts exhibited insignificant trends. The outcomes of this study offer valuable insights for agriculture, related sectors, and contribute to the food and energy security considerations for the six districts in the Bundelkhand region and regions with similar physiography.

Variations in Precipitation at the Shimantan Reservoir, China

Global warming substantially intensifies hydrologic cycles, causing increasing frequency and magnitude of catastrophic floods and droughts. Understanding the patterns and mechanisms of precipitation in historical periods is pivotal for regional disaster prevention and mitigation. Here, we analyzed the daily precipitation of six stations at the Shimantan Reservoir from 1952 to 2013 to examine precipitation characteristics at different time scales. The Mann–Kendall test, moving t-test, and Innovative Polygon Trend Analysis (IPTA) were employed to detect the trends and change points in total precipitation amount, frequency, and duration. Influences of atmospheric circulations on precipitation were then explored via cross-wavelet analysis. Our results showed increased average precipitation and decreased precipitation days annually at the Shimantan Reservoir in the past decades. Specifically, increased seasonal precipitation was only detected in summer, while precipitation days were mainly reduced in winter. There was a noticeable increasing to decreasing transition trend in precipitation from July to August, and a transition from decreasing to increasing from June to July in precipitation days. Summer rainfall was predominantly moderate and light, accompanied by shortening and highly fluctuating rainstorm durations. July exhibited the highest precipitation frequency and always experienced rainstorms. The Arctic Oscillation and East Asian summer monsoon showed positive and negative correlations, respectively, with the changes in precipitation at the Shimantan Reservoir. Our analyses provide a fine-scale portrait of precipitation patterns and mechanisms under a changing climate and benefit regional flood control and sustainable development.

Spatial and temporal patterns of indicators of climate change and variability in the Arab world in the past four decades

A comprehensive assessment of the spatial and temporal patterns of the most common indicators of climate change and variability in the Arab world in the past four decades was carried out. Monthly maximum and minimum air temperature and precipitation amount data for the period 1980–2018 were obtained from the CHELSA project with a resolution of 1 km2, which is suitable for detecting local geographic variations in climatic patterns. This data was analyzed using a seasonal-Kendall metric, followed by Sen’s slope analysis. The findings indicate that almost all areas of the Arab world are getting hotter. Maximum air temperatures increased by magnitudes varying from 0.027 to 0.714 °C/decade with a mean of 0.318 °C/decade while minimum air temperatures increased by magnitudes varying from 0.030 to 0.800 °C/decade with a mean of 0.356 °C/decade. Most of the Arab world did not exhibit clear increasing or decreasing precipitation trends. The remaining areas showed either decreasing or increasing precipitation trends. Decreasing trends varied from −0.001 to −1.825 kg m−2/decade with a mean of −0.163 kg m−2/decade, while increasing trends varied from 0.001 to 4.286 kg m−2/decade with a mean of 0.366 kg m−2/decade. We also analyzed country-wise data and identified areas of most vulnerability in the Arab world.

Climate of Syria Based on Cordex Simulations: Present and Future

AbstractRegional climate models are widely used to assess current and future impacts of climate change. In this study, we evaluate the performance of regional climate models from the Coordinated Regional Climate Downscaling Experiment programme integrated over the following three CORDEX domains: AFR, MNA and WAS. Four meteorological variables (temperature, precipitation, solar radiation and cloud cover) were evaluated over Syria at a grid spacing of 0.44°. The performance of five models in simulating the present climate characteristics (1989–2008) is evaluated with respect to the observations: CRU, ERA5 reanalysis and SARA and CLARA satellite data. We find that the mini-ensemble captures well the general spatial patterns and annual cycles of the selected variables. Anotheraim of this study was to assess the expected change of the mentioned four climate variables over Syria under the moderate emission scenario (RCP4.5) and the high emission scenario (RCP8.5) in the near future (2031–2050) and in the far future (2080–2099) with respect to the present climate (1989–2008). The simulations show a decreasing trend in cloud cover (between 6% and 10%) and precipitation (up to 9%) by mid and late century, regardless of the forcing scenarios. The simulations show a pronounced warming over Syria, which is expected to reach 6 °C by the end of the twenty-first century following the high greenhouse gas concentration scenario (RCP8.5). Furthermore, such an increase, combined with a decrease in precipitation, will shift Syria’s climate towards a more arid one.

Long-Term Trends of Extreme Climate Indexes in the Southern Part of Siberia in Comparison with Those of Surrounding Regions

Siberia, which experienced disastrous heat waves in 2010 and 2012, is one of the regions in which extreme climate events have occurred recently. To compare the long-term trends of extreme climate events in the southern part of Siberia with those of surrounding regions, we calculated 11 extreme climate indexes from observational data for 1950–2019 and analyzed the trends in Siberia and other parts of Russia using statistical techniques, i.e., Welch’s t-test, the Mann–Kendall test, Sen’s slope estimator, and a cluster analysis. We clarified that high-temperature events in March are more frequent in Siberia than in the surrounding areas. However, the increasing trends of high temperatures in Siberia were lower than those in northwestern China and Central Asia. The intensity of heavy precipitation is increasing in Siberia, as it is in the surrounding areas. Compared to the surrounding areas analyzed in previous studies, the trend of heavy precipitation in Siberia has not increased much. In particular, Siberia shows a more remarkable decreasing trend in heavy precipitation during the summer than other regions. The dry trends in the summer, however, do not occur in Siberia as a whole, and the opposite trend of summer precipitation was observed in some areas of Siberia.

Evaluation of annual total precipitation in the transboundary Euphrates–Tigris River Basin of Türkiye using innovative graphical and statistical trend approaches

The Euphrates–Tigris River Basin (ETRB), one of the largest river basins in the Middle East, is also among the most risky transboundary basins in the world. ETRB has a critical importance for the region both politically and economically due to its location. Evaluating the increasing regional impacts of climate change is even more important for the sustainable management of water and soil resources, especially in transboundary basins such as ETRB. Türkiye is one of the most important riparian countries of the ETRB and the Türkiye part of ETRB constitutes the headwater of the basin. In this study, the temporal variability of the annual total precipitation data for the period 1965–2020 of eighteen stations located in the Türkiye part of the ETRB was investigated. Classical Mann–Kendall (MK) test was used to statistically determine the monotonic trend of precipitation. In addition to the MK method, analyses were carried out with three innovative trend methods, which have the ability to interpret trends both statistically and graphically. These innovative trend methods are Şen innovative trend analysis (Şen-ITA), Onyutha trend test (OTT) and trend analysis with combination of Wilcoxon test and scatter diagram (CWTSD). The results obtained show that there is a decreasing trend in annual total precipitation in ETRB according to all trend methods generally used for the examined period. In addition, the results obtained from the relatively new OTT and CWTSD methods show strong consistency with the results of the other two methods. The advantages such as performing numerical and visual trend analysis with innovative OTT and CWTSD methods, identifying trends in low–medium–high value data and detecting sub-trends have shown that these methods can be used as an alternative to the widely used MK and Şen-ITA.

Recent precipitation trends in Peninsular Spain and implications for water infrastructure design

Study regionPeninsular Spain. Study focusThere is strong evidence that climate change has produced a decrease in precipitation combined with an increased frequency, intensity and magnitude of high-intensity storm events in Peninsular Spain. Such events have been particularly recurrent on the Spanish Mediterranean coast in recent years. This study’s first objective is to update the trends in the magnitude and seasonality of precipitation in Spain from 1951 to 2019 at different time scales. Secondly, we analyse how extreme precipitation events recorded in recent years can modify water infrastructure design flows. A QGIS plugin was programmed using Python to calculate the design flows in accordance with the methodologies legally established in Spain. New hydrological insights for the regionThe results confirm the decreasing trend in annual precipitation in most of the Spanish territory. This decrease was particularly significant during March and June. Moreover, the average increases of around 30–40 % in design flows, which reached double the values obtained in the reference period of 1951–1990 in some basins, confirm the relevance of incorporating high-intensity storm events recorded in recent years into flow calculations in Peninsular Spain. Design flows obtained without using the most recent rainfall data can be underestimated, with profound risk implications. Therefore, there is a sufficient technical basis to draw attention to this problem and recommend its formal consideration by competent authorities.

Analysis of maximum precipitation in Thailand using non‐stationary extreme value models

AbstractNon‐stationarity in heavy rainfall time series is often apparent in the form of trends because of long‐term climate changes. We have built non‐stationary (NS) models for annual maximum daily (AMP1) and 2‐day precipitation (AMP2) data observed between 1984 and 2020 years by 71 stations and between 1960 and 2020 by eight stations over Thailand. The generalized extreme value (GEV) models are used. Totally, 16 time‐dependent functions of the location and scale parameters of the GEV model are considered. On each station, a model is selected by using Bayesian and Akaike information criteria among these candidates. The return levels corresponding to some years are calculated and predicted for the future. The stations with the highest return levels are Trad, Samui, and Narathiwat, for both AMP1 and AMP2 data. We found some evidence of increasing (decreasing) trends in maximum precipitation for 22 (10) stations in Thailand, based on NS GEV models.

Decreasing summer monsoon precipitation during the Mid-Pleistocene transition revealed by a pollen record from lacustrine deposits of the Northeast Plain of China

The Mid-Pleistocene transition (MPT) was characterized not only by the transition of ice volume periodicities from 40 kyr to 100 kyr, but also by major changes in high latitude ice sheets, global sea level and CO2 / ocean carbon storage after ∼900 ka, which had a major influence on the evolution of the East Asian summer monsoon (EASM). However, there are different views regarding the trend of East Asian summer monsoon precipitation during the MPT and its driving mechanism. Together with published paleomagnetic and 26Al/10Be isotopic chronologies, we used pollen analysis of the lacustrine sediments of a drill core to reconstruct the vegetation history of the Northeast Plain of China. The results demonstrate a pattern of vegetation succession from coniferous and broadleaved mixed forest dominated by Pinus to woodland-steppe during the MPT, indicating a change from a semi-humid to a semi-arid climate. Palynological records from the Liaodong Peninsula, North China Plain, and the Tibetan Plateau also indicate a drying climate during the MPT, which was related to the decreasing trend of EASM precipitation. We suggest that falling global sea level caused by the expansion of high-latitude ice sheets, and the resulting the exposure of continental shelves and the increased transport distance of oceanic water vapor to the continental interior, was the main cause of the reduction in EASM precipitation. The weakening of the Atlantic meridional overturning circulation and the southward movement of the Intertropical Convergence Zone in the tropical Pacific may have been additional causes of the decrease in EASM precipitation.

Area Changes and Influencing Factors of Large Inland Lakes in Recent 20 Years: A Case Study of Sichuan Province, China

Lakes are important natural resources closely related to human survival and development. Based on PIE cloud computing platform, the study uses Landsat images and the empirical normalized water body index (ENDWI) to extract water body information of the large lakes in Sichuan province from 2000 to 2020 in the drought and rainy seasons, respectively, and uses the Mann–Kendall test to obtain the long-term trends of their area and climate. On this basis, the evolution of the lakes and their correlation with climate and human activities are analyzed. The results show that (1) In the past 20 years, the area of Lugu Lake, Qionghai Lake, and Luban Reservoir represent a decreasing trend, with Lugu Lake being the most affected. The area of Ma Lake, Three Forks Lake, and Shengzhong Reservoir increased, with the area of Shengzhong Reservoir increasing significantly; (2) During the drought season, all six lakes showed a decreasing trend in precipitation, with the most apparent decreasing trend for Lugu Lake (Slope = −0.8). Only Lugu Lake showed a decreasing trend in precipitation (Slope = −0.15) during the rainy season. The precipitation of Ma Lake, Three Forks Lake, Luban Reservoir and Shengzhong Reservoir showed a significant increasing trend (Slope value was greater than 1.96); (3) The temperatures of the remaining lakes all decreased in the drought season and increased in the rainy season, except that the temperature of Shengzhong Reservoir decreases throughout the year; (4) The area change of plain lakes is greatly affected by human activities, but the area of plateau lakes is are more impacted by climate. Our study improved the accuracy of long-term water body change monitoring with PIE-Engine Studio. Besides, the findings would provide reference for the implementation of sustainable water resources management in Sichuan Province.

Changes in precipitation and discharge in a Mediterranean catchment as a response to climate change and human activities

Abstract The Mediterranean region is considered to be highly affected by climate change with rainfall deficits leading to a significant decrease in river discharge. This study aims to assess the impacts of climate change on water resources in a Mediterranean catchment, namely the Bas-Loukkos catchment (Morocco), where pressure on the water resources is already present due to intensive hydro-agricultural development and is likely to increase. Mann–Kendall, Pettitt and Buishand tests were used to analyze trends and detect breakpoints in discharge and precipitation time series over the period 1960–2018. The precipitation–specific discharge relationships has been analysed by the double-mass curve (DMC). The analyses highlighted a decreasing trend in precipitation. A significant breakpoint was detected in early 1970s, with mean annual precipitation decreasing by 16–26% after this period. Discharge decreased by approximately 35% beginning in the late 1970s/early 1980s. The DMC showed different patterns between ‘undisturbed’ sub-catchments and two intensively managed sub-catchments. Wettest Mediterranean catchments are often considered as future water reservoirs to support part of the water needs in arid catchments. This study highlights that such catchments may already be impacted by climate changes, with discharge decreasing, and by water human activities that exert a major pressure on water resources.

Observed and predicted precipitation variability across Pakistan with special focus on winter and pre-monsoon precipitation.

This study utilises ground, satellite and model data to investigate the observed and future precipitation changes in Pakistan. Pakistan Meteorological Department's (PMD) monthly precipitation data set along with the Tropical Rainfall Measuring Mission (TRMM) monthly dataset TRMM_3B43 (0.25° × 0.25° resolution) and European Centre for Medium-Range Weather Forecasts's (ECMWF) monthly reanalysis product ERA5 have been used to evaluate rainfall trends over the climatic zones of Pakistan through Mann-Kendall test, Sen's slope estimator and innovative trend analysis for the time period 1978-2018. Community Climate System Model (CCSM4) projections have been employed to explore the projected changes in precipitation until 2099. Furthermore, TRMM and CCSM4 projections have been correlated and validated using root mean square error (RMSE) and mean bias error (MBE). There is a good correlation between TRMM and PMD ground observation at all stations of the country for all seasons, with correlation coefficient values ranging from 0.89 (November) to 0.97 (July and August). However, ERA5 monthly precipitation tends to overestimate rainfall in the winter months. The study shows a decreasing trend in winter precipitation in all zones of the country with a significant decrease over western mountains, i.e. zone C of the country. During 2008-2018, a sharp decrease in winter precipitation is observed as compared to the baseline value of 1978-2007 in all climatic zones. Rainy days have also shown a decrease in winter and pre-monsoon seasons. There seems to be a shift in precipitation from winter towards pre-monsoon season as pre-monsoon precipitation in the last 11years increased in all zones except for zone C. Coherently, there is a decrease in an area affected by winter precipitation and an increase in area for pre-monsoon precipitation. Future precipitation estimates from the CCSM4 model for RCP 4.5 and RCP 8.5 overestimate precipitation in most parts of the country for the first 9 observed years (2010-2018) and predict a rise in precipitation by 2099 which is more pronounced in the northern and western Pakistan while a decrease is predicted for the plains of the country, which might have negative consequences for agriculture.

Long-term latitudinal effects of precipitation change in global monsoon regions

Global paleomonsoon precipitation evolution is confined to asynchronous responses to global monsoons to shared forcings, including summer insolation, sea surface temperature, atmospheric circulation coupling, and ocean circulation. However, most studies are based on conclusions drawn from single or a few discrete records or deduced from top-down climate models, which limits our ability to understand the latitudinal effect of monsoon precipitation. In particular, precipitation is a locally constrained climate factor. Here, we present a comprehensive assessment of global monsoon precipitation over the last 12,000 cal year BP based on modern observations, paleoclimate simulations, paleoclimate records, and monsoon precipitation reconstructions over the past 12,000 cal year BP based on a bottom-up algorithm called climate field reconstruction approaches. The results show that the middle latitude monsoon precipitation is in line with the evolution of the insolation and significant long-term decreasing (increasing) trends in low latitude monsoon precipitation have not occurred over the last 12,000 years BP. For modern monsoon evolution, the monsoon precipitation also changes along the meridional direction, with overall decreasing precipitation in the global monsoon region and increasing precipitation in the monsoon margin area. Monsoon systems at different latitudes all record eight Holocene weak precipitation events, including the Younger Dryas (12,900 cal year BP to 11,700 cal year BP), which can be considered a strong effect caused by a significant reduction or collapse of a meridional ocean circulation system, namely, the Atlantic Meridional Overturning Circulation. Moreover, the low- and middle-latitude monsoon precipitation lags by approximately 2,000 years behind the onset of North Atlantic warming. Taken together, our findings provide important insights into the latitudinal effect of monsoon precipitation at different locations.

Spatial and temporal patterns of agrometeorological indicators in maize producing provinces of South Africa

Climate change impacts on maize production in South Africa, i.e., interannual yield variabilities, are still not well understood. This study is based on a recently released reanalysis of climate observations (AgERA5), i.e., temperature, precipitation, solar radiation, and wind speed data. The study assesses climate change effects by quantifying the trend of agrometeorological indicators, their correlation with maize yield, and analyzing their spatiotemporal patterns using Empirical Orthogonal Function. Thereby, the main agrometeorological factors that affected yield variability for the last 31 years (1990/91–2020/21 growing season) in major maize production provinces, namely Free State, KwaZulu-Natal, Mpumalanga, and North West are identified. Results show that there was a significant positive trend in temperature that averages 0.03–0.04 °C per year and 0.02–0.04 °C per growing season. There was a decreasing trend in precipitation in Free State with 0.01 mm per year. Solar radiation did not show a significant trend. Wind speed in Free State increased at a rate of 0.01 ms−1 per growing season. Yield variabilities in Free State, Mpumalanga, and North West show a significant positive correlation (r > 0.43) with agrometeorological variables. Yield in KwaZulu-Natal is not influenced by climate factors. The leading mode (50–80% of total variance) of each agrometeorological variable indicates spatially homogenous pattern across the regions. The dipole patterns of the second and the third mode suggest the variabilities of agrometeorological indicators are linked to South Indian high pressure and the warm Agulhas current. The corresponding principal components were mainly associated with strong climate anomalies which are identified as El Niño and La Niña events.

Groundwater-surface water interaction revealed by meteorological trends and groundwater fluctuations on stream water level

The importance of considering groundwater (GW) and surface water (SW) as a single resource of two interconnected components has rapidly increased during the last decades. To investigate GW-SW interaction in an aquifer system exploited by several pumping wells, an integrated continuous monitoring of the hydrological conditions was carried out. The sub-catchment (14 km2), located in the Aspio basin near Ancona (Central Italy), is drained by a small stream named Betelico, and it is characterised by the presence of an unconfined alluvial aquifer and a semi-confined limestone aquifer. The aim of this study is to evaluate the drivers of stream drying up occurred during the last couple of years. This has been achieved by applying a trend analysis on rainfall, air temperatures, piezometric and stream level, and well pumping rates. Precipitation trends were analysed over a 30-years period through the calculation of the Standard Precipitation Index (SPI) and through heavy rainfall events frequency plots, while the correlation between piezometric stream levels and pumping rate was analysed during the last six years. The groundwater level was compared with the stream baseflow level, highlighting the interconnection between GW-SW over the years. The analysis on the water surplus (WS) trend, together with the rainfall events characterisation, supports the hypothesis of the decrease in recharge rate as the main driver of the stream drying up. This case study stresses the importance of studying GW-SW interactions in a continuously changing climatic context characterised by a decreasing precipitation trend, coupling both the advantages of a robust method like trend analysis on time series and the field continuous monitoring.

Differences of Precipitation Characteristics among GCMs over Southeast Asia under AR6 Climate Change Scenarios

Southeast Asia is known globally as a highly vulnerable climate change region. Precipitation is the primary factor that impacts livelihood in this region due to recurring flood and drought incidents. Variables projections under climate change can be made using General Circulation Models (GCMs). An investigation of projected precipitation with the new phase of the model experiment, the Sixth Assessment Report (AR6), is worth to be considered. This study investigates the spatial distributions of variability, trend and conditions (wet/dry) of precipitations generated using 10 GCMs over the SEA under AR6 with four scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8). Three statistical methods, coefficient of variation (CV), Mann-Kendall test (MK) and standardized anomaly index (SAI), were calculated by grid cells. Significant differences among GCMs could be seen in the results. High precipitation variation with CV was indicated around the southern part of Indonesia and the Philippines oceans for six models, whereas only one model (MRI-ESM2) returned strong variation for mainland countries. A decreasing precipitation trend during the historical period could be observed in mainland countries with four GCMs. However, the SSP3-7.0 and SSP5-8.5 of most models presented precipitation increment. The extremely wet and dry ratio to all other years was calculated. Highly wet years higher than 10% were indicated in SSP5-8.5 with MPI-ESM1 occurring in most areas of the region, whereas other models gave 6-10% of highly wet occurrence. Drought situation occurred higher than 10% and could be seen with only three models with small areas under all scenarios.  returned strong variation for mainland countries. A decreasing precipitation trend during the historical period could be observed in mainland countries with four GCMs. However, the SSP3-7.0 and SSP5-8.5 of most models presented precipitation increment. The extremely wet and dry ratio to all other years was calculated. Highly wet years higher than 10% were indicated in SSP5-8.5 withMPI-ESM1 occurring in most areas of the region, whereas other models gave 6-10% of highly wet occurrence. Drought situation occurred higher than 10% and could be seen with only three models with small areas under all scenarios.

Upper Rio Grande Basin Water-Resource Status and Trends: Focus Area Study Review and Synthesis

HighlightsUpper Rio Grande Basin increased population by 80% with flat public supply water withdrawals from 1980 to 2015.Significant decreasing trends in precipitation, snowmelt rate, streamflow, baseflow, and ET were observed.Simulated near-native streamflow was greater than previous estimates, particularly for higher flow years.More precipitation as rain, slower snowmelt, less streamflow, and greater baseflow fraction impact water security.Abstract. The Upper Rio Grande Basin (URGB) is a critical international water resource under pressure from a myriad of climatic, ecological, infrastructural, water-use, and legal constraints. The objective of this study is to provide a comprehensive assessment of the spatial distribution and temporal trends of selected water-budget components (snow processes, evapotranspiration (ET), streamflow processes, and groundwater storage) using integrated analyses, such as watershed modeling and water availability and use data in the URGB over the past three decades. A spatially distributed snow evolution modeling system simulated snowpack processes over 34 years (1984–2017). It highlighted snow water equivalent declines from -35 to -77 mm/decade with widespread variability across elevation zones and land cover types. Gridded actual ET data from the SSEBop model were developed and tested for the URGB and demonstrated that all land-cover types had significant decreasing trends (1986-2015) ranging from -14 to -80 mm/decade. Conductivity-mass-balance (CMB) hydrograph separation results found that baseflow forms a large component of total streamflow, ranging from 29 to 69% (49% average) of total streamflow at 17 URGB sites upstream of Albuquerque, NM. Three of 4 graphical hydrograph separation methods in the U.S. Geological Survey Groundwater Toolbox were found to be inappropriate for estimating baseflow in the URGB; the most promising method, baseflow index (BFI) Standard, was optimized using CMB data and tested at three URGB sites, with resulting overestimation of 0 to 47%. Simulated changes in groundwater storage were extracted from historical and recent groundwater-flow models of select alluvial basins (San Luis, Española, Middle Rio Grande, and Tularosa-Hueco). In general, decreases in groundwater storage were observed from 1903 to 2013 except for the San Luis alluvial basin (Colorado), where periods of recovery are observed. The PRMS hydrologic model was successfully calibrated for 9 near-native subbasins (Nash-Sutcliffe efficiency 0.47 to 0.85) and parameters translated to the remaining subbasins; compared to simulated near-native flows (with minimal influence of reservoirs or diversions), observed Rio Grande streamgage flows demonstrated reductions of 40% or more for New Mexico and Texas areas of the basin. Significant decreasing trends (1980-2015) in precipitation, snowmelt rate, streamflow, and baseflow were observed at many of the 12 streamgage basins studied, which suggests that the decreasing trends for actual ET may be related to overall decreasing water availability in the basin, with negative implications for agricultural production and groundwater abstraction. Water security concerns arise from our findings of higher fraction precipitation as rain, slower snowmelt rates leading to decreasing streamflow production, and an increasing fraction of baseflow, all of which will affect the timing and magnitude of water available for human needs in the basin. Keywords: Baseflow, Evapotranspiration, Groundwater, Snow, Streamflow, Watershed model, Water supply.