Weakening of Indian Summer Monsoon Rainfall due to Changes in Land Use Land Cover

Abstract

Weakening of Indian summer monsoon rainfall (ISMR) is traditionally linked with large-scale perturbations and circulations. However, the impacts of local changes in land use and land cover (LULC) on ISMR have yet to be explored. Here, we analyzed this topic using the regional Weather Research and Forecasting model with European Center for Medium range Weather Forecast (ECMWF) reanalysis data for the years 2000-2010 as a boundary condition and with LULC data from 1987 and 2005. The differences in LULC between 1987 and 2005 showed deforestation with conversion of forest land to crop land, though the magnitude of such conversion is uncertain because of the coarse resolution of satellite images and use of differential sources and methods for data extraction. We performed a sensitivity analysis to understand the impacts of large-scale deforestation in India on monsoon precipitation and found such impacts are similar to the observed changes in terms of spatial patterns and magnitude. We found that deforestation results in weakening of the ISMR because of the decrease in evapotranspiration and subsequent decrease in the recycled component of precipitation.

Figure 1. Land Use and Land Cover (LULC) changes in India in recent decades.

(a) LULC map for 1987 (b) and 2005 (c) Changes (%) in Leaf Area Index in 2005 from 1987. Maps are prepared with ArcGIS10.0 (http://www.esri.com/software/arcgis/arcgis-for-desktop). The LULC from 1987 is obtained from AVHRR, and from 2005 is obtained from MODIS.

Figure 2. Evaluation of regional simulations by Weather Research and Forecasting (WRF) model.

(a) The domain considered for WRF simulations, (b) IMD meteorologically homogeneous regions, (c) Bias in regional model simulation without nudging and (d) with spectral nudging. (e–l) The scatter plots between WRF simulations (with and without nudging) and observed precipitation for all India and its different homogeneous regions (e–l). The period considered here is 2000–2010, and the LULC considered is for 2005. Maps are prepared with MATLAB R2012b (http://in.mathworks.com/products/new_products/release2012b.html). The observed precipitation data are obtained from the India Meteorological Department.

Figure 3. Changes in Monsoon Precipitation due to changes in LULC and their consistency with the declining patterns of ISMR.

Simulated average monsoon precipitation with (a) 1987 and (b) 2005 LULC and (d) their differences, which are consistent with observed changes in ISMR (c) from the 1980s to the 2000s. PDFs representing the spatial variability of changes or differences with different LULC are presented for all India and its different homogeneous regions (e–l). Maps are prepared with MATLAB R2012b (http://in.mathworks.com/products/new_products/release2012b.html).

Figure 4

Differences in (a) ET, (b) recycled precipitation, (c) number of days with CAPE>0, and (d) convective precipitation between the regional simulations with 1987 and 2005 LULC, during the period 2000–10. Maps are prepared with MATLAB R2012b (http://in.mathworks.com/products/new_products/release2012b.html).