Analysis of temperature data over semi-arid Botswana: trends and break points

Climate change is a global challenge which impacts negatively on sustainable rural livelihoods, public health and economic development, more especially for communities in Southern Africa. Assessment of indices that signify climate change can inform formulation of relevant adaptation strategies and policies for the communities. Diurnal temperature range (DTR) is acknowledged as an expedient measure of the scourge as it is sensitive to variations in radiative energy balance. In this study, a long-term (1961–2010) daily temperature data obtained from nine (9) synoptic stations in Botswana were analyzed for monotonic trends and epochal changes in annual maximum (T_max), minimum (T_min) temperatures and DTR time series. Most of the considered stations were along the Kalahari Transect, a region which is at high risk of extensive environmental change due to climate change. Mann–Kendall trend and Lepage tests were applied for trend and change point analysis, respectively. The statistical analysis shows that stations in the southern part of the country experienced significant negative trends in annual DTR at the rate of ‑0.09 to ‑0.30 °C per decade due to steeper warming rates in annual T_min than annual T_max trends. On the contrary, stations in the northern part of the country experienced positive trends in annual DTR brought about by either a decreasing annual T_min trend which outstripped annual T_max or annual T_max which outpaced annual T_min. The increasing trends in DTR varied from 0.25 to 0.67 °C per decade. For most of the stations, the most significant annual DTR trends change point was in 1982 which coincided with the reversal of atmospheric circulation patterns.