Monsoon rainfall forecasting for different hydrological regions of Bangladesh using climate predictability tool (CPT)

Abstract

This study aimed to use the Climate Predictability Tool (CPT) to analyse the monthly rainfall data over Bangladesh during 1981-2010. This technique based on a canonical correlation regressions to extract information from the large data sets.Long term changes of monsoon rainfall over Bangladesh have been studied using the available historical data collected by the Bangladesh Meteorological Department (BMD).Rainfall dataset were analyzed with Kriging interpolation method to calculate the aerial mean precipitation over Bangladesh. Correlation between observed and CPT- generated all-Bangladesh June-August (JJA) mean-rainfall during the period of 1981-2010 was found very strong (R2=0.908). The JJA mean rainfall of observed datasets of 26 stations was 14.11 mm/d in 2011, whereas, CPT generated forecast was 13.82 mm/d. Mean monsoon (June-August) rainfall was calculated for the 8 hydrological regions of Bangladesh by taking average of the stations lies within them. In case of the northwest hydrological region, strong correlation (R2=0.89) was found between observed and CPT-generated JJA mean rainfall during the period 1981-2010. Observed JJA mean rainfall (10.11 mm/d) in the northwest hydrological region in 2011 was higher compared to CPT-generated forecast (9.05 mm/d). The correlation between observed and CPT-generated JJA mean rainfall during the period 1981-2010 in the north central hydrological region was also found strong (R2=0.84). Observed JJA mean rainfall (12.89 mm/d) in the north central hydrological region in 2011 was lower compared to CPT-generated forecast (13.84 mm/d). The correlation between observed and CPT-generated JJA mean rainfall during the period 1982-2009 in the northeast hydrological region was found moderately strong. Observed JJA mean rainfall (18.66 mm/d) in the northeast hydrological region in 2011 was lower compared to CPT-generated forecast (19.49 mm/d). The correlation between observed and CPT-generated JJA mean rainfall during the period 1981-2010 in the southwest hydrological region was found strong (R2=0.8).In addition, the correlation between observed and CPT-generated JJA mean rainfall during the period of 1981-2010 in the eastern hilly hydrological region was also found strong (R2=0.821). The monsoon rainfall during JJA season in the north central, and the eastern hilly hydrological region was in increasing trend whereas, in the northwest, the south central, and the southeast hydrological regions were in decreasing trend. Hence, it can be concluded that CPT is an affordable tool for monsoon rainfall forecasting over Bangladesh.