Examining precipitation based climate indices trends for Northwest Indiana watersheds

Located in the southern tip of Lake Michigan, Northwest Indiana has many large industries with busy I 80-94 interstate corridor. Historic dunes national park is located in this region. Lake, Porter and LaPorte counties are in the northwest Indiana and most of the watersheds drain to Lake Michigan. Long term trends in precipitation based climate indices were performed using Mann Kendall Test as well as by clustering the regional data using Self Organizing Maps (SOM) by considering 113 years of historic daily precipitation data. Trends in Maximum one-day precipitation (RX1), Maximum 5-day precipitation (RX5), Simple precipitation intensity index (SDII), consecutive dry days (CDD), consecutive wet days (CWD) were examined for this region along with monthly trends. Further, relative entropy (RE) and seasonality Ratio (SR) were also examined for the changes in the distribution of precipitation. By definition, RE explains the uniformity of precipitation in an annual scale. If it is close to zero, the precipitation is well distributed throughout the year. If it is close to 8.515, then single event contributes to entire annual sum. Regional behavior was analyzed by performing data clusters using SOM. An insight about these changing trends were very crucial in water resources and water quality management and mitigating floods. This comprehensive study indicates statistically significant increasing annual rainfall trends in all the three counties of this region. Precipitation in April, July and Aug months showed statistically significant increasing trends in Lake and Porter counties. While RX1 and RX5 did not show any significant trends, RE showed a decreasing tend in the recent time period. These changes were also examined by splitting the entire 113 year spans to decades and they were compared with flow trends.