For sustainable climate hazard management, climate information at the local level is crucial for developing countries like Ethiopia, which has an exceptionally low adaptive capacity to changes in climate. As a result, rather than making local decisions based on findings from national-scale studies, the study area's research gap of local level climate variability and trend was investigated within the endorheic Lake Hayk basin for the historic series from 1986 to 2015 to scientifically show climate change/variability implications on Lake Hayk water level variations. To achieve the study objective, the precipitation, station and ERA5 reanalysis temperature and patchy lake level fused with remote sensed water extents were examined using various statistical approaches.
The major findings revealed less variable (CV= 16.66%) and statistically nonsignificant declining trends (-33.94 mm/decade) in annual precipitation. Belg and Bega seasonal precipitation showed highly variable (CV = 43.94-47.46%) nonsignificant downward trends of 4.57 mm and 22 mm per decade respectively, whereas kiremt precipitation showed moderate variability (CV=23.80%) and increased nonsignificantly at a rate of 21.89 mm per decade. Annual and seasonal mean temperatures exhibited less variable but statistically significant rising trends ranging from +0.20 to +0.45°C each decade. The lake's water level showed less variable nonsignificant rising trends (70 mm to 120 mm per year) on annual and seasonal scales between 1999 and 2005. The lake's surface area has decreased from 2243.33 ha in 2005 to 2165.33 ha in 2011. During 2011-2015, it likewise demonstrated a high variable (CV > 30%) statistically significant dropping trend ranging from -250 mm to -340 mm per year on annual and seasonal periods.
The study discovered that the endorheic lake basin was dominated by variable and diminishing precipitation, as well as continuous warming trends, particularly in recent years. It is argued that this climatic state was having a negative impact on Lake Hayk's substantially dropping water level, necessitating an immediate basin-based water management decision to save Lake Hayk from extinction.