Meteorological Predictors of Droughts in Vermont, New Hampshire, and Eastern New York

Droughts in the northeast United States can harm socio-economic activities and the ecosystems as drier conditions are out of the norm in such a region that is dependent on constant water supply. Recent climate studies demonstrate that precipitation across the northeast United States increased since the 1964-1967 droughts. However, some studies highlight that anthropogenic climate change may lead to greater interannual variability of soil moisture, with moist events followed by dry periods. Consequently, understanding the nature of droughts in the region of Vermont, New Hampshire, and eastern New York becomes increasingly important. Hence, this study was designed to address those concerns and evaluate recent changes.

The analysis is conducted using ERA5-reanalyzed surface parameters from 1979 to 2018, calculating anomalies in 32 different monthly parameters. Subsequently, multiple linear regression is used to understand which of the variables’ anomalies have the largest impact on total summer soil-moisture anomaly. In agreement with most drought indices, which are based mostly on temperature and precipitation, summer soil moisture is found to be heavily affected by precipitation and temperature, with precipitation having the largest contribution. Yet, other summer variables such as air dryness, wind speed, and cloud cover have meaningful impacts on the soil conditions and could lead to errors in the drought indices calculations. Moreover, this research highlighted how the soil moisture in the area of Vermont, New Hampshire, and eastern New York is also affected by the climate and meteorological conditions occurring during the previous winter season, which can be crucial in the forecast and preparation of eventual future droughts.

In addition to examining meteorological factors contributing to annual soil-moisture anomalies, long-term trends in soil-moisture anomalies are also examined. The computed tendencies display that, over the last 40 years, soil moisture and precipitation show no significant trends, albeit recent summers are found to have, on average, a higher soil moisture content. Temperature increases of almost one degree Celsius are seen, however, with a larger increase during the winter compared to the summer. Therefore, on average the typical seasonal variation in temperature and soil moisture between summer and winter is decreasing. Winters nowadays are warmer and can, in theory, allow more water to infiltrate the ground, helping to increase the summer soil moisture against the drying effect of warmer temperatures. Droughts, like the one in 2016, may become more frequent and/or intense in the future as temperatures continue to rise and winter dynamics change, which could lead to significant impacts on water availability in the region.