dc.description.abstract |
Drought is a natural phenomenon that occurs because of climate change. Droughts are
localized events influenced by climatic variables such as precipitation, evapotranspiration, and
temperature. As a result, the characteristics and implications of drought differ depending on
the climatic administrations in various regions around the world. Drought is one of the
maximum significant intervals in Sri Lanka. Sri Lanka is very sensitive to the effects of climate
change. Drought is an extremely considerable interval in Sri Lanka in terms of people
concerned and helps provided, and the country also serves as a recent example for drought
interval and risk assessment in tropical regions.
This research investigates the probable use of drought indices at Kirindi Oya and Kelani River
basins and provides drought assessment for future climatic scenarios.
This research was directed to perceive the changes in drought, their consistencies according to
seasonal analysis in the Kirindi Oya and Kelani River basin in Sri Lanka using normalized
difference vegetation index (NDVI), standardized precipitation index (SPI), and streamflow
drought index (SDI) for future climate change RCP 8.5 which is one of the worst scenarios
according to 5
th
assessment report of the intergovernmental panel on climate change (IPCC).
The drought assessment has been divided into three-time intervals such as observed period
(1985-2015), mid-century (2040-2059), and end-century (2080-2099). Further, future climate
rainfall data has been forecasted by bias correction monthly factor of historical climate rainfall
and observed rainfall data using linear scaling.
The NDVI has been calculated by using Landsat images near-infrared (NIR) and RED bands
in GIS 10.3. Initially, SPI and SDI have been calculated for observed rainfall and streamflow
data respectively. Hydrological model HEC-HMS was set up and calibrated (2002-2006) with
a root mean square error standard deviation ratio (RMSE std dev) value of 0.6, nash sutcliffe
(NSE) value of 0.59, and percent bias (PBIAS) of 7.63%. The model was validated from 2010
to 2014 with an RMSE std dev value of 0.7, NSE value of 0.51, and PBIAS of 3.22% for
Kirindi Oya basin. Further, for the Kelani basin. the HEC-HMS was set up and calibrated
(1990-1995) with an RMSE std dev value of 0.6, NSE value of 0.64, and PBIAS of 0.64% and
validated (2007-2011) with RMSE std dev value of 0.7, NSE value of 0.56 and Percent Bias
of -3.27% for Kelani basin. Thereafter, mid and end-century SPI and SDI have been calculated
for future bias-corrected rainfall data and future simulated streamflow, respectively.
To achieve the objectives of this research work, The rate of recurrence of drought occurrences
was determined using a combined SPI and SDI evaluation which identified 1989, 1990, 1992,
2001, and 2004 as a severe drought-affected year in the Kirindi Oya river basin in this observed
interval. For the Kelani River basin, severe drought has been identified during 1990, 2001,
2012, 2013, and 2014 in the observed interval.
According to seasonal analysis, the probability of occurrence of extreme drought according to
SPI values in Kirindi Oya basin is decreasing 25% for mid and 50% end-century, in the Kelani
basin 93.75% for mid and 68.75% in end-century. According to SDI values in the Kirindi Oya
basin is decreasing 25% for mid and 25% end-century, in the Kelani basin 93.75% for mid and
50% in end-century. First inter monsoon has been found more severe to drought for both SPI
and SDI combination in Kirindi Oya river basin, the northeast monsoon period is the driest
season for the Kelani River basin which is situated in wet zone in Sri Lanka. |
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