|COBB, STACY - University Of Georgia|
|OUYANG, YING - Us Forest Service (FS)|
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2016
Publication Date: 7/1/2016
Citation: Feng, G.G., Cobb, S., Abdo, Z., Fisher, D.K., Ouyang, Y., Adeli, A., Jenkins, J.N. 2016. Trend analysis and forecast of precipitation, reference evapotranspiration and rainfall deficit in the Blackland Prairie of eastern Mississippi. Agricultural and Forest Meteorology. 55:1425-1439.
Interpretive Summary: Sound water management planning and cropping system design can be achieved with an understanding of the statistical properties of long-term records of major climatic parameters such as rainfall and evapotranspiration. This study analyzed trends in monthly, seasonal, and annual precipitation, ETo and water deficit at a site in Macon, Noxubee county in the Blackland Prairie of Mississippi over a 120-year period (1894–2014). The mean annual rainfall was 1307 mm, varying from 660 mm to 1959 mm, with 37% of total rainfall occurring during the crop growing season from May to September for this region. Unlike rainfall, ETo did not show significant variation with time. The mean annual ETo was 1210 mm, and varied from 1101 mm to 1372 mm. Monthly ETo from April to September ranged from 117 mm to 154 mm, while rainfall ranged from 83 mm to 126 mm. Monthly rainfall deficit ranged from -22 mm to -62 mm from May to October. A mix of positive and negative trends was observed at various temporal scales. An upward trend during the months of January, April, and June to November, winter, summer, and fall and annual rainfall were observed, however, only those trends in September and fall were significant at a 95% confidence level. Rainfall increased by 0.35 mm each August and 1.06 mm in the fall every year. The insignificant downward trends in the months of February, March, May, and December, and spring were detected. In contrast, the decreasing trends were found for most months except February to April, all seasons, and annual ETo. The significant downward trends in ETo were observed in the months of January, May to October, and summer and fall. The decline in ETo ranged from 0.05 mm to 0.29 mm each year. Only one significant increasing trend in dryness index of 0.054 was found in August though all remaining months except April also exhibited upward trends. Fall and annual trends in dryness index decreased by 0.006 and 0.001, respectively. Monthly and annual ARIMA models were developed for prediction of rainfall, ETo and DI in the future. These models forecast 1319 mm of mean annual rainfall, 1203 mm of mean annual ETo, and 0082 of mean annual DI from 2015 to 2024. This study demonstrated how to determine time series trends and develop a forecast model using long-term historical weather data for a given region. Results obtained from such research can be used to develop water management strategies and practices at various spatial and temporal scales.
Technical Abstract: Trend analysis and estimation of monthly and annual precipitation, reference evapotranspiration (ETo) and rainfall deficit are essential for water resources management and cropping system design. Rainfall, ETo, and water deficit patterns and trends in eastern Mississippi USA for a 120-year period (1894-2014) were analyzed for annual, seasonal, and monthly periods. The analysis showed historical average annual rainfall, ETo, and Dryness Index (DI) in the region to be 1307 mm, 1210 mm, and 0.97, respectively. Monthly rainfall and ETo ranged from 72 to 118 mm, and 94 to 146 mm, respectively, between May and October, which resulted in a monthly rain deficit of 22 to 62 mm. Annual rainfall showed an increasing trend of 1.17 mm yr-1 while annual ETo exhibited a decreasing trend of -0.51 mm yr-1, resulting in an annual DI reduction of 0.001 per year. Seasonal trends were found for rainfall in the fall (1.06 mm yr-1), ETo in summer (-0.29 mm yr-1) and fall (-0.18 mm yr-1), and DI (-0.006). An AutoRegressive, Integrated, and Moving Average (ARIMA) approach was used to develop monthly and annual models to predict rainfall, ETo, and DI in the future. The ARIMA models forecasted 1319 mm of mean annual rainfall, 1203 mm of mean annual ETo, and 0.082 of mean annual DI from 2015 to 2024. The results and models obtained from this research can guide development of water management practices and cropping systems at various spatial and temporal scales.