Past and future changes in frost day indices in Catskill Mountain region of New York

Abstract

Changes in frost indices in the New York's Catskill Mountains region, the location of water supply reservoirs for New York City, have potentially important implications. Frost day is defined as a day with T[subscript min] < 0 °C. The objective of this study was to investigate past and predicted changes in minimum temperature (T[subscript min]) and six frost indices in the Catskill Mountains covering six reservoir watersheds. Studied frost indices included (1) number of frost days, (2) number of months with frost, (3) last spring freeze date (LSF), (4) first fall freeze date (FFF), (5) growing season length (GSL), and (6) frost season length. Past changes in the frost indices were studied using observed daily T[subscript min] for each watershed for the periods 1960–2008. Future changes in frost indices for the periods (2045–2065 and 2080–2100) were studied for emission scenarios (A1B, A2, and B1) downscaled from global climate models GCMs). Results indicated a general increase in average Tmin and GSL and a decrease in number of frost days, months with frost, frost season length, earlier LSF, and later FFF from the historical to the future periods, and the magnitude of change varied among the watersheds and GCMs. For the period 1960–2000, in all watersheds (except Cannonsville), LSF occurred earlier by 2.6–4.3 days/decade, FFF occurred later by 2.7–3.2 day/decade, and GSL was longer by 2.4–4 day/decade. Among the scenarios and GCMs, LSF occurred earlier by 4–11 and 4.5–15 days/decade for the periods 2045–2065 and 2081–2100, respectively; FFF occurred later by 1–10 and 4–13 days/decade for the periods 2045–2065 and 2081–2100, respectively; and GSL was longer by 10–25 and 13–40 days/decade for the periods 2045–2065 and 2081–2100, respectively. The increase in GSL is expected to affect hydrologic, ecosystem, and biogeochemical processes with increased net primary productivity and a resulting increase in total annual evapotranspiration.