Application of the standardised precipitation evapotranspiration index to identify drought and wet periods in Western Polesie

Abstract

The paper used monthly precipitation and temperature values to analyse climatic water conditions in Western Polesie, Poland. Annual precipitation was 540 mm, ranging from 347 to 746 mm in 2003 and 2009, respectively. Evapotranspiration averaged 458 mm over the multiannual period, ranging from 427 to 491 mm in wet and dry years, respectively. Standardised precipitation evapotranspiration index (SPEI) was calculated based on weighted averages for 1981–2020 at different periods. Based on time steps including 6-, 12-, and 24-month periods, periods with varying levels of wetness were distinguished. The average frequency of dry and wet periods was 30.2% and 29.4%, respectively. Four intense drought periods were identified: 1982–1985, 1990–1993, 2002–2005, and 2018– 2020. Drought was often associated with low monthly and annual precipitation, below 20 and 450 mm, respectively. Another factor contributing to drought was low winter precipitation and the high summer temperatures. Intense wet periods occurred in 1981–1982, 1998–2002, 2008–2012, and 2013–2015. Wet periods were often associated with heavy monthly and annual precipitation totals, above 150 mm and 650 mm, respectively. In the 21st century, the frequency, duration and magnitude of dry and wet periods increased significantly. This increase indicates greater climatic variability. Water resources need to be increased and adaptation measures introduced in response to predicted climate change in the region.