Space–time variability in soil moisture  droughts in the Himalayan region

Abstract. Soil water is a major requirement for biomass production and, therefore, one of the most important factors for agriculture productivity. As agricultural droughts are related to declining soil moisture, this paper examines soil moisture drought in the transboundary Koshi River basin (KRB) in the central Himalayan region. By applying the J2000 hydrological model, daily spatially distributed soil moisture is derived for the entire basin over a 28-year period (1980–2007). A multi-site and multi-variable approach – streamflow data at one station and evapotranspiration data at three stations – was used for the calibration and validation of the J2000 model. In order to identify drought conditions based on the simulated soil moisture, the soil moisture deficit index (SMDI) was then calculated, considering the derivation of actual soil moisture from long-term soil moisture on a weekly timescale. To spatially subdivide the variations in soil moisture, the river basin is partitioned into three distinct geographical regions, namely trans-Himalaya, the mountains, and the plains. Further, the SMDI is aggregated temporally to four seasons – winter, pre-monsoon, monsoon, and post-monsoon – based on wetness and dryness patterns observed in the study area. This has enabled us to look at the magnitude, extent, and duration of soil moisture drought. The results indicated that the J2000 model can simulate the hydrological processes of the basin with good accuracy. Considerable variation in soil moisture was observed in the three physiographic regions and across the four seasons due to high variation in precipitation and temperature conditions. The year 1992 was the driest year and 1998 was the wettest at the basin scale in both magnitude and duration. Similarly, the year 1992 also has the highest number of weeks under drought. Comparing the SMDI with the standardised precipitation index (SPI) suggested that SMDI can reflect a higher variation in drought conditions than SPI. Our results suggested that both the occurrence and severity of droughts have increased in the Koshi River basin over the last 3 decades, especially in the winter and pre-monsoon seasons. The insights provided into the frequency, spatial coverage, and severity of drought conditions can provide valuable contributions towards an improved management of water resources and greater agricultural productivity in the region.

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Space-time variability of soil moisture droughts in the Himalayan region

10.5194/hess-2020-337 ◽

2020 ◽

Author(s):

Santosh Nepal ◽

Saurav Pradhananga ◽

Narayan Kumar Shrestha ◽

Sven Kralisch ◽

Jayandra Shrestha ◽

...

Keyword(s):

Soil Moisture ◽

River Basin ◽

Hydrological Model ◽

Himalayan Region ◽

Spatial And Temporal Variation ◽

Four Seasons ◽

Spatial Coverage ◽

Drought Conditions ◽

Koshi River Basin ◽

J2000 Model

Abstract. Soil water is a major requirement for biomass production and therefore one of the most important factors for agriculture productivity. As agricultural droughts are related to declining soil moisture, this paper examines soil moisture drought in the transboundary Koshi River basin in the Central Himalayan region. By applying the J2000 hydrological model, daily spatially distributed soil moisture is derived for the entire basin over a 28-year period, 1980–2007. A multi-site and multi-variable approach – streamflow data at one station and evapotranspiration data at three stations – was used for the calibration and validation of the J2000 model. In order to identify drought conditions based on the simulated soil moisture, the Soil Moisture Deficit Index (SMDI) was then calculated, considering the derivation of actual from long-term soil moisture on a weekly timescale. To spatially sub-divide the variations in soil moisture, the river basin is partitioned into three distinct geographical areas, trans-Himalaya, the high and middle mountains, and the plains. Further, the SMDI is aggregated temporally to four seasons – winter, pre-monsoon, monsoon, and post-monsoon – based on wetness and dryness patterns observed in the study area. The results indicate that the J2000 model can simulate the hydrological cycle of the basin with good accuracy. Considerable variation in soil moisture was observed in the three physiographic regions and across the four seasons due to high variation in precipitation and temperature conditions. Droughts have been increasing in frequency in the later years of the period under study, most visibly in the pre-monsoon season. Comparing the SMDI with the standardized precipitation index (SPI) suggests that SMDI can reflect a higher variation of drought conditions than SPI. The novel contribution of this study is that a spatial and temporal variation of SMDI is calculated for the first time in the Central Himalayan region and for the Koshi River basin. This calculation is based on a high-resolution spatial representation of soil moisture, which was simulated using a fully distributed hydrological model. Our results suggest that both the occurrence and severity of droughts have increased in the Koshi River basin over the last three decades, especially in the winter and pre-monsoon seasons. The insights provided into the frequency, spatial coverage, and severity of drought conditions can provide valuable inputs towards an improved management of water resources and greater agricultural productivity in the region.

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Space-time variability of soil moisture based drought in the transboundary Koshi river basin of the Himalayan region

10.5194/egusphere-egu2020-22049 ◽

2020 ◽

Author(s):

Santosh Nepal ◽

Saurav Pradhananga ◽

Narayan Shrestha ◽

Jayandra Shrestha ◽

Manfred Fink ◽

...

Keyword(s):

Soil Moisture ◽

Water Resources ◽

River Basin ◽

Agricultural Productivity ◽

Agricultural Drought ◽

Himalayan Region ◽

Severe Drought ◽

Post Monsoon ◽

Koshi River Basin ◽

J2000 Model

<p>Soil moisture is an important part of the vegetation cycle and a controlling factor for agriculture. Withstanding the role of agricultural productivity in economic development of a nation, it is imperative that water resources planners and managers are able to assess and forecast agricultural drought. As agricultural drought is related to declining soil moisture, this paper studies the dynamics of soil moisture based drought in the transboundary Koshi river basin in the Himalayan region. By applying the J2000 hydrological model, the daily soil moisture is derived for the whole basin for a 28-year time frame (1980-2007). The soil moisture deficit index (SMDI) is calculated based on a fully distributed spatial representation by considering the derivation from the long term soil moisture on a weekly time scale. In order to analyze the variation of soil moisture drought spatially, the river basin is subdivided into three distinct geographical areas, i.e. Northern Tibet, High and Middle Mountains, and Southern Plain. Further, temporally the SMDI is calculated for four distinct seasons based on wetness and dryness patterns observed in the study area, i.e. monsoon, post-monsoon, winter and pre-monsoon. A multi-site and multi-variable (streamflow at one station and evapotranspiration at three stations) approach was used for the calibration and validation of the J2000 model. Results show that the J2000 model is able to simulate the hydrological cycle of the basin with high accuracy. The model properly represents the winter drought of 2005 and 2006 was the most severe drought in the 28-year time period. Results also show considerable increases in the frequency of pre-monsoon and post-monsoon soil moisture drought in recent years. Severe droughts have had a high frequency in recent years, which is also reflected by an increase of areas that were impacted. In summary, our results show that severity and occurrence of agricultural drought has increased in the Koshi river basin in the last three decades, especially in the winter and pre-monsoon. This will have serious implications for agricultural productivity and for water resources management of the basin.</p>

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Impacts of climate change on the hydrological regime of the Koshi river basin in the Himalayan region

Journal of Hydro-environment Research ◽

10.1016/j.jher.2015.12.001 ◽

2016 ◽

Vol 10 ◽

pp. 76-89 ◽

Cited By ~ 58

Author(s):

Santosh Nepal

Keyword(s):

Climate Change ◽

River Basin ◽

Hydrological Regime ◽

Himalayan Region ◽

Koshi River Basin ◽

Impacts Of Climate Change

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Impact of Climate Change on the Snow Hydrology of Koshi River Basin

Journal of Hydrology and Meteorology ◽

10.3126/jhm.v9i1.15580 ◽

2016 ◽

Vol 9 (1) ◽

pp. 28-44 ◽

Cited By ~ 6

Author(s):

A. Khadka ◽

L.P. Devkota ◽

R.B. Kayastha

Keyword(s):

Climate Change ◽

River Basin ◽

Climate Change Impacts ◽

Baseline Period ◽

Himalayan Region ◽

Climate Change Scenarios ◽

Snow Hydrology ◽

Monsoon Flow ◽

Change Impact ◽

Koshi River Basin

Koshi river basin which is one of the largest river basins of Nepal has its headwaters in the northern Himalayan region of the country covered with perennial snow and glaciers. Increased warming due to climate change is most likely to impact snowpack of this Himalayan region. Snowmelt Runoff Model, a degree day based method, was used in this study to assess the snowmelt hydrology of the five sub-basins, viz. Tamor, Arun, Dudhkoshi, Tamakoshi and Sunkoshi of the Koshi river basin, with and without climate change impacts. The model has been fairly able to simulate the flow. Daily bias-corrected RCM data of PRECIS-ECHAM05 and PRECIS-HadCM3 for the period of 2041-2060 were used for future projection. A period of 2000-2008 was set as baseline period to evaluate changes in future flow. In climate change scenarios, magnitude and frequency of peak flows are expected to increase and snowmelt contribution to total river flows are likely to be more. Simulated flow results indicate that the annual flow would still be governed by monsoon flow even in the future under the climate change impact. A high probability of having more flows and snowmelt in 50’s decade than that in 40’s decade is seen. The estimated future flow by ECHAM05 is found more than those estimated by HadCM3 both seasonally and annually.Journal of Hydrology and Meteorology, Vol. 9(1) 2015, p.28-44

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Spatio-temporal variation of surface soil moisture over the Yellow River basin during 1961–2012

Proceedings of the International Association of Hydrological Sciences ◽

10.5194/piahs-368-391-2015 ◽

2015 ◽

Vol 368 ◽

pp. 391-396

Author(s):

R. Tong ◽

X. Yang ◽

L. Ren ◽

H. Shen ◽

H. Shan ◽

...

Keyword(s):

Soil Moisture ◽

River Basin ◽

Surface Soil ◽

Yellow River ◽

Soil Layer ◽

Yellow River Basin ◽

The Yellow River ◽

Surface Soil Moisture ◽

Basin Scale ◽

The Yellow River Basin

Abstract. Soil moisture plays a significant role in agricultural and ecosystem development. However, in the real world soil moisture data are very limited due to many factors. VIC-3L model, as a semi-distribution hydrological model, can potentially provide valuable information regarding soil moisture. In this study, daily soil moisture contents in the surface soil layer (0–10 cm) of 1500 grids at 0.25 × 0.25 degree were simulated by the VIC-3L model. The Mann-Kendall trend test and Morlet wavelet analysis methods were used for the analysis of annual and monthly average surface soil moisture series. Results showed that the trend of surface soil moisture was not obvious on the basin scale, but it varied with spatial and temporal conditions. Different fluctuation amplitudes and periods of surface soil moisture were also discovered on the Yellow River basin during 1961 to 2012.

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Drought Assessment in the São Francisco River Basin Using Satellite-Based and Ground-Based Indices

Remote Sensing ◽

10.3390/rs13193921 ◽

2021 ◽

Vol 13 (19) ◽

pp. 3921

Author(s):

Franklin Paredes-Trejo ◽

Humberto Alves Barbosa ◽

Jason Giovannettone ◽

T. V. Lakshmi Kumar ◽

Manoj Kumar Thakur ◽

...

Keyword(s):

Soil Moisture ◽

River Basin ◽

Mitigation Strategies ◽

Agricultural Drought ◽

Extreme Drought ◽

Severe Drought ◽

Sao Francisco River ◽

São Francisco River ◽

Groundwater Drought ◽

Drought Conditions

The São Francisco River Basin (SFRB) plays a key role for the agricultural and hydropower sectors in Northeast Brazil (NEB). Historically, in the low part of the SFRB, people have to cope with strong periods of drought. However, there are incipient signs of increasing drought conditions in the upper and middle parts of the SFRB, where its main reservoirs (i.e., Três Marias, Sobradinho, and Luiz Gonzaga) and croplands are located. Therefore, the assessment of the impacts of extreme drought events in the SFRB is of vital importance to develop appropriate drought mitigation strategies. These events are characterized by widespread and persistent dry conditions with long-term impacts on water resources and rain-fed agriculture. The purpose of this study is to provide a comprehensive evaluation of extreme drought events in terms of occurrence, persistence, spatial extent, severity, and impacts on streamflow and soil moisture over different time windows between 1980 and 2020. The Standardized Precipitation-Evapotranspiration Index (SPEI) and Standardized Streamflow Index (SSI) at 3- and 12-month time scales derived from ground data were used as benchmark drought indices. The self-calibrating Palmer Drought Severity Index (scPDSI) and the Soil Moisture and Ocean Salinity-based Soil Water Deficit Index (SWDIS) were used to assess the agricultural drought. The Water Storage Deficit Index (WSDI) and the Groundwater Drought Index (GGDI) both derived from the Gravity Recovery and Climate Experiment (GRACE) were used to assess the hydrological drought. The SWDISa and WSDI showed the best performance in assessing agricultural and hydrological droughts across the whole SFRB. A drying trend at an annual time scale in the middle and south regions of the SFRB was evidenced. An expansion of the area under drought conditions was observed only during the southern hemisphere winter months (i.e., JJA). A marked depletion of groundwater levels concurrent with an increase in soil moisture content was observed during the most severe drought conditions, indicating an intensification of groundwater abstraction for irrigation. These results could be useful to guide social, economic, and water resource policy decision-making processes.

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Innovative Tools for Water Quality Management and Policy Analysis: Desert and Streamplan

Water Science & Technology ◽

10.2166/wst.1999.0508 ◽

1999 ◽

Vol 40 (10) ◽

pp. 103-110

Author(s):

Carlo De Marchi ◽

Pavel Ivanov ◽

Ari Jolma ◽

Ilia Masliev ◽

Mark Griffin Smith ◽

...

Keyword(s):

Water Quality ◽

Quality Management ◽

Policy Analysis ◽

River Basin ◽

Emission Reduction ◽

Water Quality Management ◽

Water Quality Modeling ◽

Detailed Model ◽

Basin Scale ◽

Alternative Water

This paper presents the major features of two decision support systems (DSS) for river water quality modeling and policy analysis recently developed at the International Institute of Applied Systems Analysis (IIASA), DESERT and STREAMPLAN. DESERT integrates in a single package data management, model calibration, simulation, optimization and presentation of results. DESERT has the flexibility to allow the specification of both alternative water quality models and flow hydraulics for different branches of the same river basin. Specification of these models can be done interactively through Microsoft® Windows commands and menus and an easy to use interpreted language. Detailed analysis of the effects of parameter uncertainty on water quality results is integrated into DESERT. STREAMPLAN, on the other hand, is an integrated, easy-to-use software system for analyzing alternative water quality management policies on a river basin level. These policies include uniform emission reduction and effluent standard based strategies, ambient water quality and least-cost strategies, total emission reduction under minimized costs, mixed strategies, local and regional policies, and strategies with economic instruments. A distinctive feature of STREAMPLAN is the integration of a detailed model of municipal wastewater generation with a water quality model and policy analysis tools on a river basin scale.

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