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Climate impact on water in South Asia

An understanding of likely future climate is critical to river basin planning and management in south Asia. This is vital as climate change will impact water and related sectors. Temperature and potential evapotranspiration will be higher. Changes in future precipitation are uncertain and will be amplified in river flows. Security of water supply will be compromised due to longer and more severe droughts, more precipitation falling as rain rather than snow, increased seasonality of river flow and retreat of glaciers. Flood risk will increase due to more intense extreme precipitation events.

Historical analysis

CSIRO conducted an extensive review of south Asian climate studies to develop a comprehensive climate characterisation of the region. The report (Charles et al 2016) covers major whole-of-region studies, identifies regional historical trends, and reviews the historical performance and projections of global climate models, hydrological projections and downscaled projections.

Predicting the availability of water within river basins requires a robust understanding of the climate (historical and trend) as climate drives the rainfall-runoff modelling. There are many existing global/regional daily rainfall and temperature datasets for south Asia, we conducted a comparative analysis of some well-known datasets – India Meteorological Department (IMD), Princeton, Aphrodite, WATCH and ANUSPLIN – to understand their assumptions, limitations and constraints – through comparison. The purpose of this work was not to recommend the use of one dataset over another as that is dependent on need and circumstances. Rather it was to evaluate their usability across a range of scales – region, basin and sub-catchment. This analysis has many applications. It has provided a foundation to underpin the allocation of climate datasets to hydrological modelling across the SDIP. A set of 30 indices characterising climate variables and extreme conditions were derived and mapped over the region.

These datasets have been used for consistent modelling across south Asia to characterise the hydroclimate of the region and to model future climate and hydrology impacted by climate change and other drivers. The results have been used to supplement local datasets in the modelling of the Indus, Koshi and Brahmani‐Baitarni River basins.

Integrated modelling informing policy, adaptation and planning

CSIRO has developed a consistent set of CMIP5 climate change projections from available global climate models to inform integrated climate‐water modelling. These results can be used to assess climate change impacts and subsequently guide adaptation and planning in water and related sectors. A summary of this work can be found in this factsheet. Already, the scaling factors have been used to derive sets of future (dry, median, wet) climate scenarios for the Brahmani-Baitarni basin models.

Climate change impact assessment can be carried out in two ways (or a combination of the two):

  • a top‐down approach where the projected changes to the climate variables (empirical scaling factors) in the database are used to scale the historical climate series to reflect a future climate series that is then used as inputs into models to predict future water availability and hydrological characteristics
  • a bottom‐up approach or sensitivity analysis of how changes in the input climate data can affect the modelled responses and risks to systems, to inform the need for and to guide climate impact‐adaptation vulnerability assessments.