Climate-induced variations in water resources observed on a regional scale – a case study of Poland

Currently observed climate changes have contributed to an increase in the frequency and intensity of extreme weather events across the globe. On one hand, many regions experience frequent and prolonged droughts; on the other, numerous areas face intense heavy rainfall, which often leads to flooding. A particularly alarming challenge for water resources arises when these phenomena occur alternately in the same region. Dry soil, especially when heavily cracked, loses its ability to absorb water efficiently. As a result, intense rainfall tends to generate surface runoff rather than replenishing the soil’s water reserves. This runoff often leads to soil erosion, decreased water retention, and an increased risk of flooding. Such conditions exacerbate water scarcity for ecosystems and human populations, posing significant risks to agriculture and other sectors reliant on stable water supplies. The long-term disruptions to hydrological cycles driven by these alternating extremes represent some of the most critical consequences of climate change.

One example of a region that has experienced both severe droughts and floods in recent years is Poland. In 2024, for instance, the country faced agricultural drought conditions for much of the spring and summer, while intense rainfall in September led to sudden river surges and flooding.

This study focuses on analysing changes in water resources in Poland, which are clearly influenced by climate change. For the study area, we analyse terrestrial water storage (TWS) based on observations from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions, as well as model data. Additionally, we examine changes in groundwater storage (GWS), which play a crucial role in providing drinking water to the region. To achieve this, we use data from measurement points within the national groundwater monitoring network, in addition to satellite data. We then identify extreme changes in TWS and GWS and look for links between these phenomena and the patterns of precipitation and evapotranspiration recorded in the region. For this purpose, we use well-established climate indices such as Standardized Precipitation Index (SPI), Standardised Precipitation-Evapotranspiration Index (SPEI), and Palmer Drought Severity Index (PDSI).

Both the satellite-based and in-situ methods revealed long-term declining trends in GWS and TWS across the country. These trends have been strongly influenced by climate change, leading to an intensification of evapotranspiration that surpasses total precipitation, rather than a decrease in precipitation itself.

The study was conducted as part of the project GRANDE-U “Groundwater Resilience Assessment through iNtegrated Data Exploration for Ukraine” (NSF Awards No. 2409395 and 2409396).