Influence of varied drought types on soil conservation service within the framework of climate change:insights from the Jinghe River Basin,China

Severe soil erosion and drought are the two main factors affecting the ecological security of the Loess Plateau,China.Investigating the influence of drought on soil conservation service is of great importance to regional environmental protection and sustainable development.However,there is little research on the coupling relationship between them.In this study,focusing on the Jinghe River Basin,China as a case study,we conducted a quantitative evaluation on meteorological,hydrological,and agricultural droughts(represented by the Standardized Precipitation Index(SPI),Standardized Runoff Index(SRI),and Standardized Soil Moisture Index(SSMI),respectively)using the Variable Infiltration Capacity(VIC)model,and quantified the soil conservation service using the Revised Universal Soil Loss Equation(RUSLE)in the historical period(2000-2019)and future period(2026-2060)under two Representative Concentration Pathways(RCPs)(RCP4.5 and RCP8.5).We further examined the influence of the three types of drought on soil conservation service at annual and seasonal scales.The NASA Earth Exchange Global Daily Downscaled Projections(NEX-GDDP)dataset was used to predict and model the hydrometeorological elements in the future period under the RCP4.5 and RCP8.5 scenarios.The results showed that in the historical period,annual-scale meteorological drought exhibited the highest intensity,while seasonal-scale drought was generally weakest in autumn and most severe in summer.Drought intensity of all three types of drought will increase over the next 40 years,with a greater increase under the RCP4.5 scenario than under the RCP8.5 scenario.Furthermore,the intra-annual variation in the drought intensity of the three types of drought becomes smaller under the two future scenarios relative to the historical period(2000-2019).Soil conservation service exhibits a distribution pattern characterized by high levels in the southwest and southeast and lower levels in the north,and this pattern has remained consistent both in the historical and future periods.Over the past 20 years,the intra-annual variation indicated peak soil conservation service in summer and lowest level in winter;the total soil conservation of the Jinghe River Basin displayed an upward trend,with the total soil conservation in 2019 being 1.14 times higher than that in 2000.The most substantial impact on soil conservation service arises from annual-scale meteorological drought,which remains consistent both in the historical and future periods.Additionally,at the seasonal scale,meteorological drought exerts the highest influence on soil conservation service in winter and autumn,particularly under the RCP4.5 and RCP8.5 scenarios.Compared to the historical period,the soil conservation service in the Jinghe River Basin will be significantly more affected by drought in the future period in terms of both the affected area and the magnitude of impact.This study conducted beneficial attempts to evaluate and predict the dynamic characteristics of watershed drought and soil conservation service,as well as the response of soil conservation service to different types of drought.Clarifying the interrelationship between the two is the foundation for achieving sustainable development in a relatively arid and severely eroded area such as the Jinghe River Basin.

Precipitation Cycles Relative to Storm Tracks, ENSO and PDO, and Drought—Continental Interior Central Western USA

Seventy-two years of central western United States precipitation data have been analyzed for storms originating 1000 to 3000 km away from four ocean moisture sources: Arctic, North Pacific, South Pacific, and Gulfs of California and Mexico. Precipitation trends were evaluated relative to precipitation phase, precipitation flux, storm track trajectory, and the sea surface temperature (SST) indices Oceanic Niño Index (ONI), and the Pacific Decadal Oscillation (PDO. The lack of correlation between SST indices with precipitation flux was evaluated. The relationships of meteorological, hydrological and snow droughts were evaluated relative to each other, to the climate change-induced temporal shifts in the timing of mountain snowpack decay, and the timing when North Pacific storm tracks shift from crossing to circumventing the Sierra Nevada Range.

Assessment of global meteorological,hydrological and agricultural drought under future warming based on CMIP6

Quantifying the changes and propagation of drought is of great importance for regional eco-environmental safety and water-related disaster management under global warming.In this study,phase 6 of the Coupled Model Intercomparison Project was employed to examine future meteorological(Standardized Precipitation Index,SPI,and Standardized Precipitation-Evapotranspiration Index,SPEI),hydrological(Standardized Runoff Index,SRI),and agricultural(Standardized Soil moisture Index,SSI) drought under two warming scenarios(SSP2-4.5 and SSP5-8.5).The results show that,across the globe,different types of drought events generally exhibit a larger spatial extent,longer duration,and greater severity from 1901 to 2100,with SPEI drought experiencing the greatest increases.Although SRI and SSI drought are expected to be more intensifying than SPI drought,the models show higher consistency in projections of SPI changes.Regions with robust drying trends include the southwestern United States,Amazon Basin,Mediterranean,southern Africa,southern Asia,and Australia.It is also found that meteorological drought shows a higher correlation with hydrological drought than with agricultural drought,especially in warm and humid regions.Additionally,the maximum correlation between meteorological and hydrological drought tends to be achieved at a short time scale.These findings have important implications for drought monitoring and policy interventions for water resource management under a changing climate.

Response of hydrological drought to meteorological drought in the eastern Mediterranean Basin of Turkey

The hydrographic eastern Mediterranean Basin of Turkey is a drought sensitive area.The basin is an important agricultural area and it is necessary to determine the extent of extreme regional climatic changes as they occur in this basin.Pearson’s correlation coefficient was used to show the correlation between standardized precipitation index(SPI)and standardized streamflow index(SSI)values on different time scales.Data from five meteorological stations and seven stream gauging stations in four sub-basins of the eastern Mediterranean Basin were analyzed over the period from 1967 to 2017.The correlation between SSI and SPI indicated that in response to meteorological drought,hydrological drought experiences a one-year delay then occurs in the following year.This is more evident at all stations from the mid-1990 s.The main factor causing hydrological drought is prolonged low precipitation or the presence of a particularly dry year.Results showed that over a long period(12 months),hydrological drought is longer and more severe in the upper part than the lower part of the sub-basins.According to SPI-12 values,an uninterrupted drought period is observed from 2002–2003 to 2008–2009.Results indicated that among the drought events,moderate drought is the most common on all timescales in all sub-basins during the past 51 years.Long-term dry periods with moderate and severe droughts are observed for up to 10 years or more since the late 1990 s,especially in the upper part of the sub-basins.As precipitation increases in late autumn and early winter,the stream flow also increases and thus the highest and most positive correlation values(0.26–0.54)are found in January.Correlation values(ranging between–0.11 and–0.01)are weaker and negative in summer and autumn due to low rainfall.This is more evident at all stations in September.The relation between hydrological and meteorological droughts is more evident,with the correlation values above 0.50 on longer timescales(12-and 24-months).The results presented in this study allow an understanding of the characteristics of drought events and are instructive for overcoming drought.This will facilitate the development of strategies for the appropriate management of water resources in the eastern Mediterranean Basin,which has a high agricultural potential.

Characterisation of Hydrological Drought and Implications for Sustainable Water Resources Management in the Sokoto-Rima River Basin (SRRB), Nigeria

Hydrological drought is usually characterised by water loss over time from both underground and surface supplies. Thus for this study, the assessment of hydrological drought was carried out by employing Cumulative Rainfall/Streamflow Anomaly as preliminary tools for the presence of drought signatures while detailed characterisation was via Streamflow Drought Index (SDI). The results revealed that hydrological drought was observed in all the stations;however, though in general, the stations could be classified as experiencing near normal drought conditions with mild drought signatures. The findings also revealed that the average streamflow deficit volume and durations of the hydrological drought severity were 1.780 Mm3 and 192 months, 1.444 Mm3 and 252 months, 3.148 Mm3 and 252 months, and 0.159 Mm3 and 372 months for Bakolori, Goronyo (pre dam construction era), Goronyo (post dam construction era) and Zobe stations, respectively. The results also revealed the relevance of flow duration curve and analysis of frequency of drought state transition for the development of scenario-based basin water resources management protocol. The coefficient of determination (R2) statistic of the developed regression models indicate that 73.3% and 86.5% variation in streamflow dynamics across the Basin can be explained by climate change variables. However, for sustainable management of water resources in the Basin, it is imperative that characterisation of hydrological drought and monitoring should employ robust indices which use improved monthly precipitation estimates under global warming scenario in addition to ensuring that there is a shift from reactive to proactive approach in order to combat hydrological risk. Hence, a robust framework that finds application both for planning mitigation actions which embody strategic, tactical and emergency components should be designed;to this end, analysis of persistence and recurrence of drought in time and determination of possible recurrent patterns are necessary.

Assessment of Hydrological Drought Using the Standardized Streamflow Index (SSFI): A Case Study of the Tien Yen River Basin of Quang Ninh Province, Vietnam

Probabilistic assessment of drought plays an important role in providing valuable information for evaluating water resources systems under drought conditions, and bivariate copulas are effective and efficient for the probabilistic assessment of drought based on joint distributions and/or joint return periods of drought characteristics. In this study, hydrological drought events and their characteristics (including duration and severity) in the Tien Yen River Basin of Quang Ninh province are detected using the Standardized Streamflow Index (SSFI). The BB8Copula is selected as the best-fit copula for hydrological drought duration and severity. Joint probabilities and joint return periods of drought duration and severity in the cases “and” and “or” are calculated based on the BB8Copula, which are employed for drought assessment. The results show that the drought events with 1-season or cross-quarter duration were more popular than others;joint probabilities and joint return periods of the detected drought events from 1962 to 2009, ranged from 0.2% to 92.2% and from 0.782 years to 315.414 years, respectively, in the case “and”, and ranged from 3.8% to 99.6% and from 0.724 years to 18.785 years, respectively, in the case “or”.

Impact of Meteorological Drought on Streamflows in the Lobo River Catchment at Nibéhibé, Côte d’Ivoire

The management of water resources in watersheds has become increasingly difficult in recent years due to the frequency and intensity of drought sequences. The Lobo River catchment, like most tropical regions, has experienced alternating wet and dry periods. These drought periods have a significant impact on the availability of water resources in the basin. The objective of this study is to analyse the impact of meteorological drought on flows in the Lobo River catchment. Therefore, using the Normalized Precipitation and Evapotranspiration Index (SPEI) and the Drought Flow Index (SDI), the characteristics of droughts were studied. The results of this study show that meteorological droughts were more frequent than hydrological droughts in the Lobo River watershed. However, the hydrological drought was longer and more intense than the meteorological drought. The greater relationship between meteorological and hydrological drought was observed at the Daloa and Vavoua station (0.43 < r < 0.50) compared to the Zuenoula station (r < 0.5). In addition, there was a resumption of precipitation and runoff between 2007 and 2013 in the basin. The study of these climatic trends would be very useful in the choice of management and adaptation policies for water resources management.

Tree-ring reconstruction of streamflow for Palgong Mountain forested watershed in southeastern South Korea

Tree-ring chronologies from pine,oak and black locust tree species were used to reconstruct annual streamflow and examine hydrological drought years for Palgong Mountain forested watershed in southeastern South Korea for the period from 1954-2015. The backward elimination multiple regression analysis provided the statistically significant predictor chronologies of streamflow. The final calibration and verification test models accounted for 84.8% and 81.6%,respectively,of the variability in streamflow observed in the gage data. Further verification of the validity of the reconstructed model was undertaken with the Pearson Correlation Coefficient,the Reduction of Error Test,and the Durbin-Watson Statistics and indicated fidelity of the model for reconstructing the annual streamflow. Analyses of the reconstructed annual streamflow indicate that the most persistent years of high flows above the median annual discharge occurred from 1986-2008.This period included 7 single or multiple years of highest flow above the 90 th percentile discharge and multiple years of high flows with a time interval of 2-6 years,although with intervening multiple years of low flows below the 10 th and 50 th percentile. In comparison,the most persistent years of low flows below the median annual discharge occurred from 1954-1985 and 2009-2015. This period included 8 single or multiple years of lowest flow below the 10 th percentiledischarge and multiple years of low flows with a time interval of 2-9 years,although also with intervening multiple years of high flows above the 50 th percentile. No single years of extreme hydrological droughts below the 10 th percentile were identified from 1986-2015 whereas a greater proportion of high flows above the 90 th percentile occurred during this period. The persistent single or multiple years of lowest flows between 1954 and 1985 were the recent most critical hydrological drought years identified in the Palgong Mountain forested watershed providing supportive evidence of the severity of past hydrological droughts during that period,applicable to the southeastern South Korea where the study watershed is located. This interpretation agrees with the hydrological drought event years identified from 1951 to the early 1980 s in a related national study that used precipitation proxy data to reconstruct past occurrences of droughts in Korea.

Low-frequency variability of terrestrial water budget in China using GRACE satellite measurements from 2003 to 2010

Mass variations in terrestrial water storage（TWS） obtained from eight years of satellite data from the Gravity Recovery and Climate Experiment（GRACE） are used to describe low frequency TWS through Empirical Orthogonal Function（EOF） analysis. Results of the second seasonal EOF mode show the influence of the Meiyu season. Annual variability is clearly shown in the precipitation distribution over China, and two new patterns of interannual variability are presented for the first time from observations, where two periods of abrupt acceleration are seen in 2004 and 2008. GRACE successfully measures drought events in southern China, and in this respect, an association with the Arctic Oscillation and El Nino-Southern Oscillation is discussed. This study demonstrates the unique potential of satellite gravity measurements in monitoring TWS variations and large-scale severe drought in China.

Comprehensive evaluation of hydrological drought characteristics and their relationship to meteorological droughts in the upper Tarim River Basin,central Asia

Comprehensive evaluation of the characteristics and mechanisms of droughts is of great significance to drought risk prediction and prevention.The 3-monthly scale Standardized Runoff Index(SRI-3)and 3-monthly scale Standardized Precipitation Evapotranspiration Index(SPEI-3)were employed herein to characterize hydrological and meteorological droughts,respectively,within the four upper subbasins of the Tarim River Basin(TRB)during 1961-2015.The propagation of droughts was also evaluated.The hydrological drought duration(Dd)and drought severity(Ds)were determined by Run theory,and Copula functions were adopted to investigate the hydrological drought probabilities and return periods.The propagation relationships of hydrological and meteorological droughts were assessed.The results indicated that:1)hydrological drought index(SRI-3)significantly increased in the TRB from 1961 to 2015;the increase was most significant in winter.Meteorological drought index(SPEI-3)exhibited a weak upward trend through time;2)the characteristics of hydrological droughts varied between the subbasins;increases in the SRI were most significant in the Yarkand and Hotan Rivers,whereas the Dd and Ds of hydrological droughts were higher in the Kaidu and Yarkand Rivers;3)Frank Copula was the most closely fitted Copula function in the four subbasins of the TRB and yielded average drought return periods of 4.86,4.78,3.72,and 5.57 years for the Kaidu,Aksu,Yarkand,and Hotan River Basins,respectively.The return periods in the four subbasins were generally less than 10 years from 1961 to 2015;4)a cross wavelet transform(XWT)exhibited a significant positive correlation between hydrological and meteorological droughts,except for the Yarkand River Basin,which exhibited a significant negative correlation.Besides,the propagation relationship of meteorological droughts to hydrological droughts showed remarkable seasonal variations.