Changes In Soil Moisture Storage Research Articles

Seasonal dynamics and spatial patterns of soil moisture in a loess catchment

Abstract. The spatial and seasonal patterns in soil moisture and the processes controlling them in semi-arid landscapes are not well understood. Loess landscapes minimize any confounding effects of variation in soil characteristics and are thus ideal for studying topographic influences on soil moisture in drylands. In this study, volumetric soil moisture was monitored monthly for 5.5 years at 20 cm intervals between the surface and 5 m depth at 89 sites across a small (0.43 km2) catchment on the Chinese Loess Plateau. The median soil moisture was computed for each month and depth for each monitoring site as a measure of the typical soil moisture conditions. Seasonal changes in soil moisture were mainly concentrated in the shallow (0–100 cm) soil, with a clear seasonal separation between wet conditions in October–March and dry conditions in May–July, even though precipitation is highest in July–August. Soil moisture was higher on the northwest-facing slopes due to increased drying from solar radiation on the southeast-facing slopes. This effect of slope aspect was greater between October and March, when the zenith angle of the sun was lower and the aspect-dependent difference in solar radiation reaching the surface was larger. The wetter, northwest-facing slopes were also characterized by larger annual soil moisture storage changes. Soil texture was nearly uniform across both slopes, and soil moisture was not correlated with the topographic wetness index, suggesting that variations in evapotranspiration dominated the spatial pattern of soil moisture in shallow soils under both wet and dry conditions. Water balance calculations indicate that over 90 % of the annual precipitation was seasonally cycled in the soil between 0 and 300 cm, suggesting that only a minor fraction infiltrates to groundwater and becomes streamflow. Our findings may be broadly applicable to loess regions with monsoonal climates and may have practical implications for catchment-scale hydrologic modeling and the design of soil moisture monitoring networks.

Quantifying basin-scale changes in groundwater storage using GRACE and one-way coupled hydrological and groundwater flow model in the data-scarce Bandung groundwater Basin, Indonesia

Assessing basin-scale groundwater storage changes is often difficult when groundwater table data are scarce. In this study, we quantify the groundwater storage changes by using the Wflow_sbm hydrological model coupled with the MODLOW groundwater model in the data-scarce area of the Bandung groundwater basin, Indonesia. The soil moisture storage change calculated by Wflow_sbm plus the groundwater storage change calculated by MODFLOW is compared to the water storage change estimated by the GRACE satellite between 2005 and 2015. The calculated cross-correlation coefficient is 0.502, and 62.1% of the simulated water storage change falls within GRACE's estimated uncertainty bounds. The important context in the water storage comparison are GRACE temporally local time-lags, data gaps in GRACE datasets, and differences in model seasonal performance and analyzed domain characteristics. The two latter factors highlight the importance of considering local groundwater-related information over large-scale global datasets in basin-scale groundwater storage change assessment. Based on the groundwater flow model, the current predicament of groundwater abstraction in the Bandung groundwater basin is highly unsustainable for future groundwater uses. On average, the groundwater storage in the study area is dwindling at the rate of 87 million m3/year between 2005 and 2018, dominantly a consequence of groundwater abstraction, whose effect is rippled to further impact the whole groundwater flow regime. Agreed by the situation shown by the limited data, the simulated groundwater table drawdown, spatially, is found to be locally and non-uniformly distributed. The capability of a one-way coupled hydrological and groundwater model to investigate basin-scale groundwater storage change, with comparable estimates to the GRACE dataset, unravel the opportunity of using such methods to estimate the behavior of future groundwater storage dynamics under the changing anthropogenic and climatic factors in catchment-scale studies.

Effect of Coffee Ages and Shade Types on Soil Moisture and Soil N, P, K Availability in UB Forest

Water and nutrients is important for plant which has its characteristics. This study has been carried out in the UB (Brawijaya University) forest about soil moisture content during rainy and dry seasons, Total-N, -P, -K from litter on different types of shade and age of coffee plants, and their effect on soil Available-N, -P, and -K. There are P1 (control), P2 (4-year-coffee + pine), P3 (7-year-coffee + pine), P4 (4-year-coffee + mahogany), and P5 (7-year-coffee + mahogany). These treatments affected to total soil moisture storage, Total-N, -P, -K of litter, and Available-N, -P, -K in the soil. The soil moisture storage change between rainy and dry seasons was 36.97 mm. The highest Total-N, -P, and -K of litter was 11.00 kg ha-1 y-1 at P3, 1.06 kg ha-1 y-1 at P2, and 4.35 kg ha-1 y-1 at P3, which was inconsistently associated with high soil nutrients. The highest Total-N was 0.40 (0-20 cm), 0.27 (20-40 cm), 0.30% (40-60 cm) at P4, Available-K was 1.69 (0-20 cm), 1.64 (20-40 cm), 1.87 cmol kg-1 (40-60 cm) at P5, and Available-P was 15.21 (0-20 cm), 14.06 (20-40 cm), 12.64 mg kg-1 (40-60 cm) at P1.

Using observed soil moisture to constrain the uncertainty of simulated hydrological fluxes

AbstractUsing data from five long‐term field sites measuring soil moisture, we show the limitations of using soil moisture observations alone to constrain modelled hydrological fluxes. We test a land surface model, Modélisation Environnementale communautaire‐Surface Hydrology/Canadian Land Surface Scheme, with two configurations: one where the soil hydraulic properties are determined using a pedotransfer function (the texture‐based calibration) and one where they are assigned directly (the hydraulic properties‐based calibration). The hydraulic properties‐based calibration outperforms the texture‐based calibration in terms of reproducing changes in soil moisture storage within a 1.6 m deep profile at each site, but both perform reasonably well, especially in the summer months. When the models are constrained using observations of changes in soil moisture, the predicted hydrological fluxes are subject to very large uncertainties associated with equifinality. The uncertainty is larger for the hydraulic properties‐based calibration, even though the performance was better. We argue that since the pedotransfer functions constrain the model parameters in the texture‐based calibrations in an unrealistic way, the texture‐based calibration underestimates the uncertainty in the fluxes. We recommend that reproducing observed cumulative changes in soil moisture storage should be considered a necessary but insufficient criterion of model success. Additional sources of information are needed to reduce uncertainties, and these could include improved estimation of the soil hydraulic properties and direct observations of fluxes, particularly evapotranspiration.

Water balance response of permafrost-affected watersheds to changes in air temperatures

Observations show increases in river discharge to the Arctic Ocean especially in winter over the last decades but the physical mechanisms driving these changes are not yet fully understood. We hypothesize that even in the absence of a precipitation increase, permafrost degradation alone can lead to increased annual river runoff. To test this hypothesis we perform 12 millennium-long simulations over an idealized hypothetical watershed (1 km2) using a distributed, physically based water balance model (Water flow and Balance Simulation Model, WaSiM). The model is forced by both a hypothetical warming defined by an air temperature increase of 7.5 ∘C over 100 years, and a corresponding cooling scenario. To assess model sensitivity we vary soil saturated hydraulic conductivity and lateral subsurface flow configuration. Under the warming scenario, changes in subsurface water transport due to ground temperature changes result in a 7%–14% increase in annual runoff accompanied by a 6%–20% decrease in evapotranspiration. The increase in runoff is most pronounced in winter. Hence, the simulations demonstrate that changes in permafrost characteristics due to climate warming and associated changes in evapotranspiration provide a plausible mechanism for the observed runoff increases in Arctic watersheds. In addition, our experiments show that when lateral subsurface moisture transport is not included, as commonly done in global-scale Earth System Models, the equilibrium water balance in response to the warming or cooling is similar to the water balance in simulations where lateral subsurface transport is included. However, the transient changes in water balance components prior to reaching equilibrium differ greatly between the two. For example, for high saturated hydraulic conductivity only when lateral subsurface transport is considered, a period of decreased runoff occurs immediately after the warming. This period is characterized by a positive change in soil moisture storage caused by the soil moisture deficit developed during prior cooling.

Two-dimensional numerical simulations of soil-water and heat flow in a rainfed soybean field under plastic mulching

Abstract Numerical simulation can help understanding water- and heat-flow systems through plastic-mulched soils. An effective simulation approach is crucial to know the role of plastic mulch in a soil ecosystem, which can save water in agriculture. A field experiment was conducted at Gifu University in a rainfed soybean cultivation under plastic mulch and bare soil treatments to clarify the soil water and heat flow mechanism. Furthermore, the two-dimensional numerical software HYDRSUS-2D model with different boundaries at the soil surface was used to simulate water and heat flows. Firstly, soil hydraulic parameters were estimated by inverse solution using laboratory-measured data and then coupled soil-water and heat flows were simulated by optimizing soil thermal parameters by inverse solution. The HYDRUS-2D model simulated water and heat flow through the root zone depths satisfactorily. The root-mean square error (RMSE) was 0.015–0.030, and 0.046–0.055 cm3 cm−3 for the plastic mulch, and bare soil, respectively, in estimating soil moisture and 0.66–1.28, and 0.70–1.54 °C, respectively in estimating soil temperature. Water infiltration was 61% lower in the plastic-mulched soil, which reduced soil evaporation as well as soil-moisture storage changes compared to bare soil. This study can be applied to design and manage different plastic mulching patterns in rain-fed crop cultivation.

A novel approach to analyze uncertainties and complexities while mapping groundwater abstractions in large irrigation schemes

While determining the water balance for large irrigation schemes, coping with complexities and uncertainties in estimation of groundwater (GW) abstraction is still a challenge. On other hand, estimating GW abstraction is of paramount importance to ensure the proper management of surface and GW resources. Although, there are number of well-known methods exist to map GW abstraction, utilization-factor (Uf) is considered as a reliable method. However, at large scales, tubewells utilization time required for Uf method is difficult to retrieve as large and small tubewells are governed under different rules. Geo-informatics is another emerging approach being used to estimate GW abstraction, however, there are several complexities and uncertainties involved in characterizing GW abstraction using satellite remote sensing imagery that leads to inaccurate end results. In current study, in-situ GW measurements were performed to calibrate and validate the GW abstraction estimated from geo-informatics approach at Lower Bari Doab Canal (LBDC) command area of the Indus basin of Pakistan. For in-situ measurements, an intensive tubewell survey was conducted at a grid size of 1 km at 30 locations situated at head, middle and tail end reaches of the LBDC. For the geo-informatics approach used in this study, GW abstraction is considered as a difference of actual evapotranspiration (ETa) from net canal water use and effective rainfall after satisfying soil moisture storage changes. Results of calibration of geo-informatics approach compared with the in-situ measurements showed R2 of 0.89, 0.81 and 0.79 at head, middle and tail end reaches, respectively. Intra-grid annual comparison of in-situ measurements showed that tubewells were being governed by different rules and thus yielded different abstraction within a grid ranging from 854 mm (±105) at head, 742 mm (±220) at middle and 649 mm (±244) at tail grids. Statistical analysis showed that annual GW abstraction by in-situ measurements at head 814 mm (±52), middle 769 mm (±44) and tail 688 mm (±56) end reaches varied significantly at a confidence interval of 95%. The spatial mapping by geo-informatics showed that farmers’ fields situated at proximity of head end reaches utilize 4% and 9% extra water than from those placed at middle and tail end reaches, respectively. The inequity of GW abstraction in LBDC command area highlighted in this study requires immediate intervention of policy makers for sustainable GW management.

Modelling the hydrological processes of Koupendri catchment Northwest, Benin

This study calibrated and validated rainfall-runoff model (WaSiM) to aid decisions on sustainable management of scarce water resources in Koupendri catchment. The model was successfully calibrated (NSE = 0.61; R2 = 0.61, RMSE = 0.63) and validated (NSE = 0.68; R2 = 0.78; RMSE = 0.57) using optimised soil and land use parameters. Though the model underpredicted some of the peak flows, the overall calibration result could be adjudged satisfactory with a p-factor of 0.94 and an r-factor of 0.93 which were all within the acceptable range of uncertainty. Evapotranspiration and discharge constituted 98%-99% of the total water balance of the catchment while the change in soil moisture storage constituted only < 2%. Surface runoff was the predominant streamflow component (86%-90%), suggesting infiltration excess overland flow as the main runoff generation mechanism for the catchment. The water balance reflected the hydro climatic conditions of the catchment with actual evapotranspiration ranging between 68% and 75% of the total annual rainfall.

Water budgeting in major rabi crops under surface irrigation in Western Indo-Gangetic Plains

A water budget confers the relationship between input, output and changes in the amount of water at an individual farm level to the watershed level depending upon point of interest. Basic components of water budgets are precipitation, evapotranspiration, change in soil moisture storage, deep percolation and runoff. However, non-availability of water balance parameter is the main problem for achieving the more crop per drop. Therefore, the current study was undertaken at ICAR-Indian Agricultural Research Institute, New Delhi farm (Mid-block, MB) during rabi 2016-17 to study the water budget of different major rabi crops (wheat, mustard, chickpea) under surface irrigation. Water budget components like soil moisture were measured by gravimetric method periodically, and daily crop-evapotranspiration (ETc) and stage-wise effective rainfall (Pe) for the test crops were estimated using FAO-CROPWAT- 8.0 model. Irrigation scheduling was done on the basis of soil moisture depletion method and total volume of water applied measured through star flow meter. The total volume of irrigation water applied during the entire crop period was 337.75, 211.54 mm and 182.90 mm, for wheat, mustard and chickpea, respectively. The results revealed that both in late- and timely - sown mustard (MB-3A-1 and 3A-2), chickpea (MB-9-A) and wheat crops (MB-3A-3, 6-A and 12-A), the highest ETc was recorded during mid-season stage (i.e. 82.90, 79.50, 94.07, 126.04, 114.02, 132.61 mm, respectively). The deep- percolation losses varied from 29.3-31.8 % for sandy loam soil to 40.2-42.2 % for clay loam soil under different crops due to larger amount of irrigation water applied in clay soil. These water budgeting parameters are location and crop specific and so to be estimated for crops, seasons and regions.

Streamflow partitioning using the Budyko framework in a northern glaciated watershed under drought to deluge conditions

We use the Budyko framework to examine streamflow changes due to climate variation and human activities in the Mauvais Coulee Basin, a 1002 km2 sub-basin that contributes streamflow to Devils Lake, a terminal lake that has experienced catastrophic flooding over the past three decades. The basin lies within the northern glaciated prairies, contains innumerable wetland complexes that follow fill-spill hydrological principles, has undergone extensive land use change to support dryland farming, and has experienced a drought to deluge hydroclimatic transition over the last century. We implement the Budyko framework to partition the runoff increase to the lake between its climatic or human components. Initial results attribute 45% of the streamflow increase to climate factors, and 55% to human activities. Implementation of the Budyko framework to examine streamflow partitioning, however, rests upon a series of assumptions that are usually not directly verified. We then examine each Budyko framework assumption to determine its suitability for our study site and study period. None of the required assumptions are fully satisfied. Our study site and study period encompass two distinct hydroclimatic modes, contain no clear single inflection point separating baseline and altered periods, experience root zone soil moisture storage changes during the study period, and exhibit a non-stationary precipitation-streamflow relationship during the transitional period between the two hydroclimatic modes. Streamflow attribution produced by the standard application of the Budyko framework is not applicable to our study site or study period. We recommend that local-scale investigations of streamflow partitioning based upon the Budyko framework be more intentional in verifying model assumptions as a standard practice in implementing the method.

Modelling the hydrological processes of Koupendri catchment Northwest, Benin

This study calibrated and validated rainfall-runoff model (WaSiM) to aid decisions on sustainable management of scarce water resources in Koupendri catchment. The model was successfully calibrated (NSE = 0.61; R2 = 0.61, RMSE = 0.63) and validated (NSE = 0.68; R2 = 0.78; RMSE = 0.57) using optimised soil and land use parameters. Though the model underpredicted some of the peak flows, the overall calibration result could be adjudged satisfactory with a p-factor of 0.94 and an r-factor of 0.93 which were all within the acceptable range of uncertainty. Evapotranspiration and discharge constituted 98%-99% of the total water balance of the catchment while the change in soil moisture storage constituted only < 2%. Surface runoff was the predominant streamflow component (86%-90%), suggesting infiltration excess overland flow as the main runoff generation mechanism for the catchment. The water balance reflected the hydro climatic conditions of the catchment with actual evapotranspiration ranging between 68% and 75% of the total annual rainfall.

How Spatial Patterns of Soil Moisture Dynamics Can Explain Field‐Scale Soil Moisture Variability: Observations From a Sodic Landscape

AbstractRoot‐zone soil moisture (0–110 cm) was monitored at 21 sites within a cold‐region semiarid prairie grazing pasture over multiple growing seasons. There were large differences in the moisture dynamics for different sites, which was related to local‐scale impacts of sodium‐induced clay dispersion. Sites with high exchangeable sodium percentages, indicative of sodic soils, were characterized by small changes in soil moisture storage. The sites with the largest soil moisture changes had negligible exchangeable sodium percentage. We used this difference to divide the area into sites that participate in the field‐scale water balance and those that do not. As a result of this heterogeneity, a unique soil moisture variability‐mean relationship was observed; the spatial variability of root‐zone soil moisture was lowest during intermediate wetness conditions and highest for wet and dry conditions. Furthermore, the shape of the variability‐mean relationship depended on the depth over which soil moisture was integrated. The persistent differences in soil moisture dynamics were also responsible for the presence of two distinct spatial patterns of root‐zone soil moisture, representing early and late growing season (i.e., wet and dry conditions). The participating versus nonparticipating framework may be applicable broadly to sodic soils and to other soil types and has practical implications for parameterizing the water balance in hydrological models and for designing representative soil moisture monitoring networks in such environments.

A new indicator framework for quantifying the intensity of the terrestrial water cycle

A quantitative framework for characterizing the intensity of the water cycle over land is presented, and illustrated using a spatially distributed water-balance model of the conterminous United States (CONUS). We approach water cycle intensity (WCI) from a landscape perspective; WCI is defined as the sum of precipitation (P) and actual evapotranspiration (AET) over a spatially explicit landscape unit of interest, averaged over a specified time period (step) of interest. The time step may be of any length for which data or simulation results are available (e.g., sub-daily to multi-decadal). We define the storage-adjusted runoff (Q′) as the sum of actual runoff (Q) and the rate of change in soil moisture storage (ΔS/Δt, positive or negative) during the time step of interest. The Q′ indicator is demonstrated to be mathematically complementary to WCI, in a manner that allows graphical interpretation of their relationship. For the purposes of this study, the indicators were demonstrated using long-term, spatially distributed model simulations with an annual time step. WCI was found to increase over most of the CONUS between the 1945 to 1974 and 1985 to 2014 periods, driven primarily by increases in P. In portions of the western and southeastern CONUS, Q′ decreased because of decreases in Q and soil moisture storage. Analysis of WCI and Q′ at temporal scales ranging from sub-daily to multi-decadal could improve understanding of the wide spectrum of hydrologic responses that have been attributed to water cycle intensification, as well as trends in those responses.

Recent changes in terrestrial water storage in the Upper Nile Basin: an evaluation of commonly used gridded GRACE products

Abstract. GRACE (Gravity Recovery and Climate Experiment) satellite data monitor large-scale changes in total terrestrial water storage (ΔTWS), providing an invaluable tool where in situ observations are limited. Substantial uncertainty remains, however, in the amplitude of GRACE gravity signals and the disaggregation of TWS into individual terrestrial water stores (e.g. groundwater storage). Here, we test the phase and amplitude of three GRACE ΔTWS signals from five commonly used gridded products (i.e. NASA's GRCTellus: CSR, JPL, GFZ; JPL-Mascons; GRGS GRACE) using in situ data and modelled soil moisture from the Global Land Data Assimilation System (GLDAS) in two sub-basins (LVB: Lake Victoria Basin; LKB: Lake Kyoga Basin) of the Upper Nile Basin. The analysis extends from January 2003 to December 2012, but focuses on a large and accurately observed reduction in ΔTWS of 83 km3 from 2003 to 2006 in the Lake Victoria Basin. We reveal substantial variability in current GRACE products to quantify the reduction of ΔTWS in Lake Victoria that ranges from 80 km3 (JPL-Mascons) to 69 and 31 km3 for GRGS and GRCTellus respectively. Representation of the phase in TWS in the Upper Nile Basin by GRACE products varies but is generally robust with GRGS, JPL-Mascons, and GRCTellus (ensemble mean of CSR, JPL, and GFZ time-series data), explaining 90, 84, and 75 % of the variance respectively in "in situ" or "bottom-up" ΔTWS in the LVB. Resolution of changes in groundwater storage (ΔGWS) from GRACE ΔTWS is greatly constrained by both uncertainty in changes in soil-moisture storage (ΔSMS) modelled by GLDAS LSMs (CLM, NOAH, VIC) and the low annual amplitudes in ΔGWS (e.g. 1.8–4.9 cm) observed in deeply weathered crystalline rocks underlying the Upper Nile Basin. Our study highlights the substantial uncertainty in the amplitude of ΔTWS that can result from different data-processing strategies in commonly used, gridded GRACE products; this uncertainty is disregarded in analyses of ΔTWS and individual stores applying a single GRACE product.

Reconstructing annual groundwater storage changes in a large-scale irrigation region using GRACE data and Budyko model

A two-parameter annual water balance model was developed for reconstructing annual terrestrial water storage change (ΔTWS) and groundwater storage change (ΔGWS). The model was integrated with the Gravity Recovery and Climate Experiment (GRACE) data and applied to the Punjab province in Pakistan for reconstructing ΔTWS and ΔGWS during 1980–2015 based on multiple input data sources. Model parameters were estimated through minimizing the root-mean-square error between the Budyko-modeled and GRACE-derived ΔTWS during 2003–2015. The correlation of ensemble means between Budyko-modeled and GRACE-derived ΔTWS is 0.68 with p-value <0.05. The ΔGWS was reconstructed by subtracting soil moisture storage change from the Budyko-modeled ΔTWS and was validated (i.e., r=0.74, p-value<0.05) against well observations during the pre-GRACE period (i.e., 1985–1994). The negative values of the cumulative sum of the reconstructed ΔGWS during 1980–2015 (i.e., −13.6±9.7cm) indicate that the aquifer in Punjab has experienced depletion. The estimated depletion rate is −0.3±0.2cm/year and it has a negative correlation (i.e., r=−0.70, p-value<0.0001) with the total number of tube wells installed in Punjab. The integration of the developed Budyko model with GRACE data provides a new way for evaluating long-term groundwater depletion in large-scale irrigation regions with parsimonious models.

Estimation of quantitative measures of total water storage variation from GRACE and GLDAS-NOAH satellites using geospatial technology

This study represents the first attempt to examine spatial and seasonal variations of the surface water budget by using the Gravity Recovery and Climate Experiment (GRACE) by measuring gravity anomalies on earth to estimate changes in Total Water Storage (TWS) content over the north-western region of the India including New Delhi and states of Rajasthan, Uttar Pradesh and Haryana, covering an area of 676,917 km2. The TWS (surface plus ground) and its changes were estimated from 2003 to 2012. Additionally, Global Land Data Assimilation System (GLDAS) variables were used to infer as to how TWS was partitioned into canopy water and soil moisture components. To evaluate monthly accumulated rainfall, Tropical Rainfall Measuring Mission (TRMM) data, processed by the Global Precipitation Climatology Center (GPCC) were used. By computing storage changes in GRACE, TWS, GLDAS land surface state variables and terrestrial-based water balance approach, we calculated groundwater storage changes. The time-series comparisons show good agreement between the GRACE satellite data, GLDAS model data and computed groundwater data. The change in soil moisture storage is less than that in saturated storage. Both the GRACE and calculated groundwater storage changes indicate storage loss in the range of 86.43 km3/y ± average of 10 years data (in terms of equivalent water thickness). The average groundwater loss for was calculated as 9.7 ± km3/y, states of Haryana as 9.7 ± km3/y, Rajasthan as 33.199 ± km3/y and Uttar Pradesh as 44.4827 ± km3/y. Our results are convincing of a credible GRACE hydrology data which can be handy in monitoring storage dynamics and water availability at regional scale. As GRACE data are available for virtually every region of the world, their application in conjunction with hydrological models will improve applications of hydrological studies which may lead not only to water balance closures, but also to sustainable water resource management at regional scale.

Variations in water storage in China over recent decades from GRACE observations and GLDAS

Abstract. We applied Gravity Recovery and Climate Experiment (GRACE) Tellus products in combination with Global Land Data Assimilation System (GLDAS) simulations and data from reports, to analyze variations in terrestrial water storage (TWS) in China as a whole and eight of its basins from 2003 to 2013. Amplitudes of TWS were well restored after scaling, and showed good correlations with those estimated from models at the basin scale. TWS generally followed variations in annual precipitation; it decreased linearly in the Huai River basin (−0.56 cm yr−1) and increased with fluctuations in the Changjiang River basin (0.35 cm yr−1), Zhujiang basin (0.55 cm yr−1) and southeast rivers basin (0.70 cm yr−1). In the Hai River basin and Yellow River basin, groundwater exploitation may have altered TWS's response to climate, and TWS kept decreasing until 2012. Changes in soil moisture storage contributed over 50 % of variance in TWS in most basins. Precipitation and runoff showed a large impact on TWS, with more explained TWS in the south than in the north. North China and southwest rivers region exhibited long-term TWS depletions. TWS has increased significantly over recent decades in the middle and lower reaches of Changjiang River, southeastern coastal areas, as well as the Hoh Xil, and the headstream region of the Yellow River in the Tibetan Plateau. The findings in this study could be helpful to climate change impact research and disaster mitigation planning.

Vegetation regulation on streamflow intra‐annual variability through adaption to climate variations

AbstractThis study aims to provide a mechanistic explanation of the empirical patterns of streamflow intra‐annual variability revealed by watershed‐scale hydrological data across the contiguous United States. A mathematical extension of the Budyko formula with explicit account for the soil moisture storage change is used to show that, in catchments with a strong seasonal coupling between precipitation and potential evaporation, climate aridity has a dominant control on intra‐annual streamflow variability. But in other catchments, additional factors related to soil water storage change also have important controls on how precipitation seasonality propagates to streamflow. More importantly, use of leaf area index as a direct and indirect indicator of the above ground biomass and plant root system, respectively, reveals the vital role of vegetation in regulating soil moisture storage and hence streamflow intra‐annual variability under different climate conditions.

Development and evaluation of a physically based multiscalar drought index: The Standardized Moisture Anomaly Index

AbstractIn this study, a new physically based multiscalar drought index, the Standardized Moisture Anomaly Index (SZI), was developed and evaluated, which combines the advantages of the Palmer Drought Severity Index (PDSI) and the Standardized Precipitation Evapotranspiration Index (SPEI). The SZI is based on the water budget simulations produced with a sophisticated hydrological model, and it also includes a multiscalar feature to quantify drought events at different temporal scales taken from SPEI. The Chinese Loess Plateau was selected to evaluate the performance of the SZI. Our evaluation indicates that the SZI accurately captures the onset, duration, and ending of a multiyear drought event through its multiscalar feature, while the PDSI, which lacks this feature, is often unable to describe the evolution of a multiyear drought event. In addition, the variability of the SZI is more consistent with observed streamflow and the satellite normalized difference vegetation index than that of the Standardized Precipitation Index and the SPEI. Although the SPEI includes potential evapotranspiration (PE) as water demand, water demand is often unrealistically estimated based solely on PE, especially over arid and semiarid regions. The improved drought quantification with the SZI is the result of a more reasonable estimation of water demand by including evapotranspiration, runoff, and any change in soil moisture storage. In general, our newly developed SZI is physically based and includes a multiscalar feature, which enables it to provide better information for drought monitoring and identification at different temporal scales.

GRACE satellite monitoring of large depletion in water storage in response to the 2011 drought in Texas

Texas experienced the most extreme one‐year drought on record in 2011 with precipitation at 40% of long‐term mean and agricultural losses of ~$7.6 billion. We assess the value of Gravity Recovery and Climate Experiment (GRACE) satellite‐derived total water storage (TWS) change as an alternative remote sensing‐based drought indicator, independent of traditional drought indicators based on in situ monitoring. GRACE shows depletion in TWS of 62.3 ± 17.7 km3 during the 2011 drought. Large uncertainties in simulated soil moisture storage depletion (14–83 km3) from six land surface models indicate that GRACE TWS is a more reliable drought indicator than disaggregated soil moisture or groundwater storage. Groundwater use and groundwater level data indicate that depletion is dominated by changes in soil moisture storage, consistent with high correlation between GRACE TWS and the Palmer Drought Severity Index. GRACE provides a valuable tool for monitoring statewide water storage depletion, linking meteorological and hydrological droughts.