Abstract
This study was conducted to evaluate the variability, trends, volatility, and transition patterns of rainfall in drought-prone northwest Bangladesh. Daily rainfall recorded at five stations for the period 1959–2018 were used for this purpose. Non-parametric tests of variability changes, a modified Mann–Kendall trend test, innovative trend analysis (ITA), a generalized autoregressive conditional heteroscedasticity (GARCH)–jump model, and a Markov chain (MC) were used to assess the variability changes, trends, volatility, and transitions in rainfall to understand the possibility of the persistence of droughts and their predictability. The results showed an overall decrease of variability in annual and seasonal rainfall, but an increase in mean pre-monsoon rainfall and a decrease in mean monsoon rainfall. This caused a decrease in pre-monsoon droughts, but few changes in monsoon droughts. The ITA and rainfall anomaly analysis revealed high temporal variability and, thus, rapid shifts in rainfall regimes, which were also supported by the volatility dynamics and time-varying jumps from the GARCH–jump model and the rapid changes in drought index from the MC analysis. Therefore, the lack of drought in recent years cannot be considered as an indicator of declining droughts in the region.
Highlights
Increased atmospheric water vapor in warmer climates has altered the seasonal and geographical variability of rainfall [1,2], which has changed the probability of rainfall extremes and hydrological disasters like floods and droughts [3]
Higher implications of a warmer climate have been found for droughts compared to other hydrological disasters [4,5,6,7] Droughts mainly affect agriculture and, the livelihoods of millions of people who are dependent on agricultural production every year [8,9,10]
The coefficients of variability in monthly rainfall during the early (1959–1988) and late (1989–2018) periods were estimated and statistical tests were conducted to evaluate the significance in the difference of variability between the two periods
Summary
Increased atmospheric water vapor in warmer climates has altered the seasonal and geographical variability of rainfall [1,2], which has changed the probability of rainfall extremes and hydrological disasters like floods and droughts [3]. The impacts of climate change on precipitation and droughts are different in different regions. An increase in rainfall reliability and, lessening of droughts have been reported in some regions [18,19]. This indicates a large spatial heterogeneity in drought trends on a global scale. The Intergovernmental Panel on Climate Change (IPCC) [20] reported a large spatial variability in drought trends. Shiru et al [14] found that droughts covering large areas are decreasing, but localized droughts with a smaller areal coverage are increasing in Nigeria
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