Shrinking ponds in subarctic Alaska based on 1950–2002 remotely sensed images

Abstract

Over the past 50 years, Alaska has experienced a warming climate with longer growing seasons, increased potential evapotranspiration, and permafrost warming. Research from the Seward Peninsula and Kenai Peninsula has demonstrated a substantial landscape‐level trend in the reduction of surface water and number of closed‐basin ponds. We investigated whether this drying trend occurred at nine other regions throughout Alaska. One study region was from the Arctic Coastal Plain where deep permafrost occurs continuously across the landscape. The other eight study regions were from the boreal forest regions where discontinuous permafrost occurs. Mean annual precipitation across the study regions ranged from 100 to over 700 mm yr−1. We used remotely sensed imagery from the 1950s to 2002 to inventory over 10,000 closed‐basin ponds from at least three periods from this time span. We found a reduction in the area and number of shallow, closed‐basin ponds for all boreal regions. In contrast, the Arctic Coastal Plain region had negligible change in the area of closed‐basin ponds. Since the 1950s, surface water area of closed‐basin ponds included in this analysis decreased by 31 to 4 percent, and the total number of closed‐basin ponds surveyed within each study region decreased from 54 to 5 percent. There was a significant increasing trend in annual mean temperature and potential evapotranspiration since the 1950s for all study regions. There was no significant trend in annual precipitation during the same period. The regional trend of shrinking ponds may be due to increased drainage as permafrost warms, or increased evapotranspiration during a warmer and extended growing season.