Liu et al. (2026) Assessing the impact of drought on water use efficiency among ecosystems on the Mongolian Plateau

Identification

• Journal: Energy Nexus
• Year: 2026
• Date: 2026-02-10
• Authors: Xinyi Liu, Quan Lai, Shan Yin, Rihe Gao
• DOI: 10.1016/j.nexus.2026.100664

Research Groups

• College of Public Administration, Inner Mongolia University of Finance and Economics, Hohhot, China
• College of Geographical Science, Inner Mongolia Normal University, Hohhot, China
• Inner Mongolia Key Laboratory of Remote Sensing and Geographic Information Systems, Inner Mongolia Normal University, Hohhot, China

Short Summary

This study investigated the responses of precipitation use efficiency (PUE), soil water use efficiency (SWUE), and groundwater use efficiency (GWUE) to meteorological, soil, and groundwater drought conditions on the Mongolian Plateau from 2000 to 2020. Findings reveal that while WUE indicators generally increased, their responses to drought varied significantly by region and vegetation type, exhibiting lagged effects ranging from 2.4 to 4.4 months, with groundwater drought often reducing GWUE, particularly in grasslands.

Objective

• To characterize the spatiotemporal trends of meteorological, soil, and groundwater drought, and of PUE, SWUE, and GWUE across major ecosystem types on the Mongolian Plateau.
• To analyze the relationships between PUE and SPEI, SWUE and SMAI, and GWUE and GWSDI, and to reveal how these relationships vary among different ecosystems and climate regimes.
• To quantify the lag duration and impact intensity of meteorological, soil, and groundwater drought on the three WUE indicators.
• To reveal the response differences of these lagged effects and drought impacts among different climatic zones and vegetation types on the Mongolian Plateau.
• To evaluate the relative changes in PUE, SWUE, and GWUE during drought versus non-drought periods.

Study Configuration

• Spatial Scale: Mongolian Plateau (Mongolia and Inner Mongolia Autonomous Region of China), covering approximately 2.74 × 10^6 square kilometers, at a spatial resolution of 0.1 degrees.
• Temporal Scale: Monthly data from 2000 to 2020 (21 years).

Methodology and Data

• Models used:
  • Water Use Efficiency (WUE) indicators: Precipitation Use Efficiency (PUE), Soil Water Use Efficiency (SWUE), Groundwater Use Efficiency (GWUE).
  • Drought indices: Standardized Precipitation Evapotranspiration Index (SPEI-1), Soil Moisture Anomaly Index (SMAI, with Box-Cox transformation), Groundwater Storage Deficit Index (GWSDI, derived from machine learning).
  • Machine Learning: Random Forest (RF) model for Groundwater Storage Anomaly (GWSA) prediction, compared with Support Vector Machine (SVM) and Back-Propagation Neural Network (BPNN).
  • Statistical methods: Sen’s slope, Mann-Kendall test, Pearson correlation coefficient.
• Data sources:
  • Vegetation types: Global Land Cover 2000 Project (GLC2000) and MODIS land cover dataset (MOD12Q1).
  • Meteorological data (2 meter air temperature, precipitation, relative humidity, sunshine duration, evapotranspiration, potential evapotranspiration): ECMWF Reanalysis v5 (ERA-5).
  • Aridity Index (AI): Calculated from multi-year mean annual precipitation and potential evapotranspiration.
  • Digital Elevation Model (DEM): Geospatial Data Cloud (30 meter resolution).
  • Vapor Pressure Deficit (VPD): Climatic Research Unit (CRU).
  • Normalized Difference Vegetation Index (NDVI): MODIS (MOD15A2H).
  • Gross Primary Productivity (GPP): Global OCO-2-based Solar-Induced Fluorescence (GOSIF) dataset.
  • Surface Soil Moisture (0–7 centimeters): ERA-5 SM product.
  • Groundwater Storage (GWS), Terrestrial Water Storage (TWS), Surface Soil Moisture (SSM, 0–10 centimeters), Root Zone Soil Moisture (RSM, 0–100 centimeters), Snow Water Equivalent (SWE), Canopy Water Storage (CWS): NASA Global Land Data Assimilation System (GLDAS-2).

Main Results

• From 2000 to 2020, PUE, SWUE, and GWUE generally exhibited upward trends across the Mongolian Plateau (57.57% for PUE, 93.90% for SWUE, 91.31% for GWUE showed positive slopes).
• Meteorological (SPEI) and soil (SMAI) drought indices predominantly indicated wetting trends (59.33% and 54.49% of the area, respectively), while the groundwater drought index (GWSDI) reflected a drying trend across most of the study area (67.47%).
• WUE indicators showed positive correlations with drought indices in arid regions, but negative correlations in humid regions.
• Significant lagged effects of drought on WUE were identified: SPEI on PUE had an average lag of 2.4 months (in 36.25% of the area), SMAI on SWUE had an average lag of 3.4 months (in over 50% of the area), and GWSDI on GWUE had the longest average lag of 4.4 months (in over 70% of the area).
• Drought typically led to increases in PUE (88.39% of area) and SWUE (81.90% of area), indicating ecosystem resistance. However, groundwater drought generally caused reductions in GWUE (61.14% of area), particularly in grasslands.
• Enhancements of GWUE under groundwater drought were observed in semi-humid forests and semi-arid sandy lands, highlighting complex and diverse ecosystem responses.

Contributions

• Provided a systematic exploration of the coupling relationships between meteorological, soil, and groundwater drought and three distinct water use efficiency indicators (PUE, SWUE, GWUE) on the Mongolian Plateau.
• Quantified the regional specificity of lagged effects and drought impacts across different climate zones and vegetation types, addressing existing knowledge gaps.
• Improved the applicability of the Soil Moisture Anomaly Index (SMAI) and Groundwater Storage Deficit Index (GWSDI) for the Mongolian Plateau by optimizing their calculation methods.
• Offered valuable insights for developing appropriate ecosystem management strategies to address the challenges posed by climate change, particularly regarding the joint management of surface and groundwater resources.

Funding

• National Natural Science Foundation of China (No. 42461049)
• Fundamental Research Funds for the Directly Affiliated Universities of Inner Mongolia Autonomous Region (No. NCYWT25005)

Citation

@article{Liu2026Assessing,
  author = {Liu, Xinyi and Lai, Quan and Yin, Shan and Gao, Rihe},
  title = {Assessing the impact of drought on water use efficiency among ecosystems on the Mongolian Plateau},
  journal = {Energy Nexus},
  year = {2026},
  doi = {10.1016/j.nexus.2026.100664},
  url = {https://doi.org/10.1016/j.nexus.2026.100664}
}