Analysis of climatic trends in climate divisions of Oklahoma, USA

We used monthly climatological datasets from the NOAA US Climate Divisional Database to detect long-term trends (1951–2021) in the nine climate divisions of Oklahoma, USA. We applied Hargreaves-Samani method to calculate reference evapotranspiration (ETo) and used 12-month standardized precipitation index to characterize meteorological droughts. Modified Mann-Kendall and Sen’s slope non-parametric trend tests were performed to identify significant (p < 0.05) positive and negative trends in maximum, average, and minimum air temperature (T max, T avg, T min, respectively), precipitation (P), and ETo on annual and seasonal time scales. Innovative trend analysis and least square regression were used to further support the results. Statistically significant positive trends were observed in annual T min in all climate divisions. Statistically significant increasing trends were also observed in T min and T avg on a seasonal scale across different climate divisions whereas significant decreasing trends were observed in summer T max. Winter P showed statistically significant increasing trends across Oklahoma. ETo only showed significant decreasing trends in the South Central climate division on an annual basis, and in central and eastern parts of the state during summers. The rate of change in temperature ranged from −0.010 to 0.020 °C/year. The rate of change in P ranged from −0.16 to 3.16 mm/year. while ETo ranged from −0.44 to 0.42 mm/year. These trends have critical implications for agricultural management to cope with potential long-term climate impacts on agricultural production, pests and invasive species, water resources, and soil moisture.