ADB IHE Delft Knowledge Partnership
Asian Development Bank - IHE Delft

Climate Change Scenario Development

India’s National Water Mission supported by the Asian Development Bank (ADB) evolved location specific strategic frameworks for the three pilot sub basins selected as focal areas for study and planning. The three pilot sub basins identified were Sutlej (Punjab) -snow fed, Kshipra (Madhya Pradesh) – groundwater and the Cauvery Delta (Tamil Nadu) – coastal. For each sub basin, strategies were developed to address present issues and projected adaptation needs. This project for Cauvery River’s Delta Zone (CDZ) is implemented under the framework of the ADB - IHE Delft Knowledge Partnership. 

UNESCO-IHE contribution to the Cauvery Delta project

UNESCO-IHE contributed to this by developing temperature, rainfall and sea level rise scenarios based on different climate change (CC) scenarios. Two reports were delivered during the project. The first one provided the climate change analyses for CDZ for time horizons up to 2050 focusing on i) available climate data from the point of view of requirements of the water sector groups, and ii)  Developing of future climate change scenarios for rainfall and temperature as the key variables for further hydrological analysis based on projections from climate models. Also data sets for other variables like humidity, wind speed, The second report focused on sea level rise and extreme events and consists of four main sections : i) Determining the current trends in local relative sea level rise (Baseline) ; ii) Developing the scenarios for local relative sea level rise by the year 2100  , iii) a description of a methodology that may be adopted to estimate the sea level change associated with extreme events, and iv) recommendations on using the presented relative sea level rise projections within the CASDP.

Sea level projections

The current trend of relative sea level rise (RSLR) was determined by analyzing available tide gauge data in the study area. Tide gauge data for Cochin, Chennai and Vishakapatnam obtained from the PSMSL were used in this study. Using the guidelines provided by Nicholls et al. (2011) were used to derive Relative Sea Level Rise (RSLR) scenarios for six (6) IPCC SRES scenarios (B1, B2, A1B, A1T, A2 and A1F1) for CDZ.  The ranges of RSLR thus calculated for the six SRES scenarios are shown in Fig. 1. The highest and lowest values of RSLR by 2100 relative to 1990 projected for the study area are 0.87m and -0.03m respectively. Note that storm surge is not included in this analysis due to the unavailability of tide gauge data.

Temperature projection

Observed data over the CDZ showed a generally increasing trend in both maximum and minimum temperatures. Maximum temperature change over the CDZ projected by the models show a range from about 1.0 to 1.5°C by 2050. Minimum temperatures show a larger increase with changes ranging from 2-3°C. Different emission scenarios did not produce large differences in temperatures changes over time-horizon until the 2050s. 

Rainfall Projection

Rainfall observations showed very little trends, with year-to-year variability being predominant. The projected rainfall changes over the region vary from model to model, but most of the results showed increase in rainfall during the main rainy season. (Figure 2)

Recommendations

The CASDP intends to implement improved drainage facilities, flood control measures and land use strategies (among others) to mitigate the potential impacts of climate change in the Cauvery Delta Zone (CDZ). Rising temperatures will have impact the water sector in terms of higher water demand and enhanced evaporative losses. Higher mean temperatures may also translate into longer spells of heat waves in summers. Although the rainfall projections are not clearly indicative of an increase in magnitude, there seems to be a shift towards a more variable behavior in daily rainfall amounts. Addressing such changes would perhaps require better management strategies that can dynamically adjust to a wider range of climate fluctuations.
In order the effectively adopt the sea level scenarios developed in the study, a simplistic method and a more elegant method based on risk considerations were recommended to the client. It was also recommended that not only the inundation hazard but also the coastal erosion hazard be considered in developing mitigation strategies.