Date of Graduation

8-2022

Document Type

Thesis

Degree Name

Master of Science in Geography (MS)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Song Feng

Committee Member

Linyin Cheng

Second Committee Member

Mohamed Aly

Keywords

Climate, GIS, Index, Models, Weather, Winter

Abstract

The objective of this study was to quantify the winter severity in a way that was reproduceable and easy to understand. The Accumulated Winter Severity Seasonal Index (AWSSI) was chosen for this reason and was used to quantify winter severity by season across the state of Arkansas. The variables that go into the AWSSI calculation are maximum daily temperature, minimum daily temperature, daily snowfall, and daily snow depth. When the snowfall and snow depth were missing, they can be estimated using daily temperature and precipitation. Then the estimated snowfall and snow depth can be subsequently used to quantify the winter severity. The AWSSI calculated this way is named as (Precipitation Accumulated Winter Severity Seasonal Index) pAWSSI. Our evaluations suggested that pAWSSI can reasonably reproduce the temporal variation of AWSSI. Due to scarce snowfall and snow depth data in Arkansas, this study used the pAWSSI to examine the spatial and temporal variations of winter severity in Arkansas from 1901-2012 based on observations and from 2012- 2100 based on multiple climate model simulations.

The long-term averaged pAWSSI suggested more harsher winter in the north and northwest Arkansas. The state averaged AWSSI suggest notable interannual variability. The most severe winters occurred in late 1970s and earlier 1980s, likely due to several severe snow storms in these years. There is an overall weak downward trend before middle 1970s, followed by notable decreasing AWSSI scores, suggesting less harsher winters in recent decades. However, the start, end, and length of winter season in AR show weak spatial and temporal variations.

The temporal variations in pAWSSI are largely controlled by winter temperature. There was less snowfall in warm winters and hence smaller pAWSSI. The decreasing pAWSSI (less cold winter) is associated with warming temperature, especially in the recent several decades. The temporal variations of pAWSSI are also influenced by large-scale atmospheric and oceanic indices. On interannual time scale, the winters with higher pAWSSI scores are usually associated with negative North Atlantic Oscillation (NAO) phases. The milder winters during 1990s and 2000s are associated with positive NAO phases. The pAWSSI is also significantly correlated with Pacific Decadal Oscillation (PDO) during 1948-2012. However, the link between PDO and pAWSSI weakened during recent two decades, suggested that the impacts of PDO on winter severity in Arkansas may change on decadal time scales.

The daily temperature and precipitation from 20 CMIP5 models under the RCP8.5 scenario were also used to evaluate the winter severity in AR in the future. The pAWSSI for individual models was calculated. The ensemble mean pAWSSI of the 20 CMIP5 models show similar long-term averaged and trend as that based on observations during 1950-2012, suggesting that the models did a reasonable job in simulating the temporal variations of pAWSSI. The models projected accelerating decreasing trend in pAWSSI from 2006-2100, suggesting that the projected climate changes can cause pronounced decrease in winter severity. Compared to the present-day condition, the pAWSSI in Arkansas may decrease 65-75% by the end of this century.

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