Crop Yield & Climate Change in Western Nepal

Assessing climate change impacts on cereal yield and irrigation water requirements using AquaCrop and CMIP6 projections.

Published in the Journal of Water and Climate Change (2025). DOI: 10.2166/wcc.2025.543

Md. Zuber*, Nabin Kalauni*, Nirman Shrestha, Vishnu Prasad Pandey, Binod Pokharal (*equal contributors)

This was my undergraduate/post-baccalaureate research project at the Center for Water Resource Studies (CWRS), IOE, studying climate change impacts on rice and wheat yield and irrigation water requirements in Tulsipur, Dang — a sub-metropolitan city in the mid-western Terai region of Nepal.

Study Area

The study area is Tulsipur, situated in the Lumbini province of Nepal (27°37′–28°29′N, 82°02′–82°54′E). The region is primarily characterized by sandy loam soils, with ~55% of arable land under monsoon rice and ~20% under winter wheat. The Satgaule Sir Kulo and Shir Kulo irrigation projects are the principal irrigation sources. Historical average annual rainfall is 1,530 mm, over 90% during the monsoon (June–September).

Methods

The AquaCrop model (FAO) was calibrated and validated at field scale using farmer survey data and soil samples collected at the study site. Future climate projections came from a multi-model ensemble of 5 CMIP6 GCMs (ACCESS-CM2, EC-EARTH3, MIROC6, MPI-ESM1-2-HR, MRI-ESM2-0) under two scenarios:

  • SSP245 (medium emissions)
  • SSP585 (high emissions)

Climate data were bias-corrected using quantile mapping (NASA NEX-GDDP-CMIP6 at 0.25° resolution). Three future periods were evaluated: near future (2021–2050), mid future (2051–2075), and far future (2076–2100).

Sixteen field management scenarios were tested, combining:

  • Irrigation: Rainfed (RF), Fully Irrigated (FI), Deficit Irrigation D1, Deficit Irrigation D2
  • Fertilization: 0%, 60%, 100%, and 150% of the National Recommended Fertilizer Dose (NRFD)

Key Findings

  • Deficit irrigation reduces water use with minimal yield loss: A D1 deficit irrigation strategy reduces net irrigation requirements by up to 81% for rice and 24% for wheat, at a cost of only ~1% reduction in yield.
  • Climate change generally increases yield and decreases water requirements for both crops across most future scenarios — except winter wheat, where water requirements are projected to increase by up to 13% in the far future.
  • Rainfed conditions produce highly variable yields, making irrigation essential for stable production.
  • Recommended strategy: Deficit irrigation D1 with 100% NRFD fertilizer dose — balances yield, water use, and climate resilience.

Projected Climate

Under SSP585, maximum temperature is projected to rise by 2.9–5.4 °C and minimum temperature by 4.6–8.8 °C in the far future. Precipitation trends are erratic, with large inter-seasonal variability. Progressive warming is expected in all seasons, with increasing irrigation pressure particularly for winter wheat.