Pangani - Development of Climate Change Scenarios

This report documents the modelled scenarios of local climate variability due to global climatic change, using the projected climate changes to modify the “no change”, 76-year long, monthly sub-catchment rainfall sequences, and average monthly evaporation values that serve as input to the hydrological catchment model that has been configured and calibrated for the Pangani Basin.

The Terms of Reference for this study were to provide modified rainfall and evaporation series for each of the selected 16 catchments in the Pangani River Basin under scenarios of climate change. Statistical downscaling was used to establish multiple linear regression (MLR) models between observed monthly rainfall and NCEP/NCAR reanalyses for the period 1961-2001.

Established models gave moderately good to better efficiencies for majority of catchments although rainfall in some months could not be better predicted. However, downscaled monthly rainfall using HadCM3 were poorly predicted and the use of GFDL CM2.1 improved significantly rainfall prediction with no predictions of negative rainfalls.

The resulting downscaled rainfall indicated significant hanges will be experienced during the months October to January leading to declining predominantly orographic rainfall in these months. An increase of rainfall is predicted during the long rains particularly in April and May and the dry season (June-September) particularly in June suggesting a protrusion of long rains into the dry season.

Calibration of MLR models for evaporation could not be achieved due to lack of time series of
evaporation and more time is required to establish the scarce available information from hardcopies. However, the highest ratio of 1.368 temperature predictions of between December-February (DJF) and June-August (JJA) and annual evaporation rise of 20% by the year 2100 were used to modify available average monthly evaporation to provide evaporation scenarios for 2020s, 2050s and 2080s.

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