Changes in spatial and temporal trends in wet, dry, warm and cold spell length or duration indices in Kansas, USA

ABSTRACT Extended periods with excessive or no rainfall or high or low temperatures have important implications on the water cycle, can stress ecosystems and can be detrimental to the economy of a region. These periods are generally studied using spell length indicators or duration indices ( SDIs ). Fourteen SDIs are calculated to study the changes in wet/dry/warm/cold spells using daily precipitation and maximum and minimum air temperature from 23 centennial weather stations spread across Kansas during four time periods (through 1920, 1921–1950, 1951–1980 and 1981–2009) and two temporal scales (annual and seasonal). Among the SDIs , 3 represent wet spells [wet spell length ( WetSL ); AvWetSL ; MaxWetSL ]; 3 for dry spells [dry spell length ( DrySL ); AvDrySL ; MaxDrySL ]; 4 for warm spells [warm spell length ( WarmSL ); average warm spell length ( AvWarmSL ); maximum warm spell length ( MaxWarmSL ); WarmSDI ] and 4 are for cold spells [cold spell length ( ColdSL ); average cold spell length ( AvColdSL ); maximum cold spell length ( MaxColdSL ); ColdSDI ]. In general, we observe that Kansas has 57–64 days year −1 in a wet spell; 302–309 days year −1 in a dry spell; ∼47 days year −1 in each warm and cold spells. The average length of a wet/dry spell is ∼1.5 days, while the warm/cold spells are for 2 days. The maximum length of a wet spell is ∼4.4 days, a dry spell is ∼35 days and warm/cold spells is ∼6 days. We found the number of wet days increasing annually. Interestingly, the warm days during winter are increasing with an overall decrease in the days in warm and cold spells across both temporal scales.