Richard W. Dixon and Todd Moore Department of Geography Texas State University San Marcos May 2009
Study Area Texas occupies about 7% of the area of the US. Second largest state at 692,000 sq. km. Lat Range: 25.83N 36.50N (1289 km) Lon Range: 93.52W 106.63W (1255 km) Elev Range: sea level 2667 m Physical Regions: Gulf Coastal Plains, Interior Lowlands, Great Plains, Basin and Range Province. Climate Types: Cfa, BS, BW
Data Sources Temperature and Precipitation: 1932 2002. US Historical Climatology Network 43 stations with long-term records. Corrected for time of observation and identified inhomogeneities. Not fully homogenous spatially.
Data Sources Bulk Evaporation: 1954 2007 Texas Water Development Board Blend of pan measurements and modified Penman formula computations. Gridded to 1 x 1 lat/lon
Texas HCN Stations Miami Muleshoe Plainview Clarksville Crosbyton Haskell Greenville Seminole Snyder Albany Weatherford Marshall Dublin Corsicana El Paso Brownwood Mexia Balmorhea Pecos McCamey Lampasas Ft. Stockton Llano Temple Alpine Blanco Brenham Boerne New Braunfels Liberty Flatonia San Antonio Luling Hallettsville Eagle Pass Beeville Danevang Encinal Alice Corpus Christi Falfurrias Rio Grande City 0 125 250 500 Kilometers
Data Processing Less than 1% missing in temperature and precipitation estimated by neighbor regression. Evaporation 100% complete. Monthly data also aggregated to seasonal and annual values. Winter (D,J,F) Spring (M,A,M) Summer (J,J,A) Fall (S,O,N).
Annual Temperature Trend (C Deg / Year) (Various POR 1932-2002) Annual Precipitation Trend (mm / Year) (POR 1932-2002) + 1.869 + 0.007-0.014-0.013-0.013-0.010-0.012-0.009-0.017-0.008 + 2.674 + 2.926 + 0.015-0.012-0.011-0.012-0.007 + 3.943 + 2.747 + 3.620 + 4.178 + 5.620-0.011 + 0.026 + 2.533 + 0.013 0 125 250 500 Kilometers 0 125 250 500 Kilometers
Spring Temperature Trend (C Deg / Year) (Various POR 1932-2002) Spring Precipitation Trend (mm / Year) (POR 1932-2002) + 0.020 + 0.019-0.021-0.017 + 0.020-0.019 + 0.035-0.013-0.012 + 0.012 + 0.011 + 0.020 0 125 250 500 Kilometers 0 125 250 500 Kilometers
Summer Temperature Trend (C Deg / Year) (Various POR 1932-2002) Summer Precipitation Trend (mm / Year) (POR 1932-2002) -0.020-0.020 + 0.013-0.020-0.017-0.020-0.014-0.016-0.012-0.010 + 1.682-0.012-0.018-0.017-0.017 + 0.006-0.028 + 0.035 + 0.016 0 125 250 500 Kilometers 0 125 250 500 Kilometers
Fall Temperature Trend (C Deg / Year) (Various POR 1932-2002) Fall Precipitation Trend (mm / Year) (POR 1932-2002) -0.015-0.017 + 2.437 + 1.565 + 1.829-0.020-0.019-0.012 + 0.016-0.017-0.019 + 0.017 + 1.770 + 1.592 + 2.960 + 1.845 + 2.301 + 3.360 + 0.012 0 125 250 500 Kilometers 0 125 250 500 Kilometers
Winter Temperature Trend (C Deg / Year) (Various POR 1932-2002) Winter Precipitation Trend (mm / Year) (POR 1932-2002) -0.019 + 0.015-0.023-0.015-0.015 + 0.045 + 0.026 0 125 250 500 Kilometers 0 125 250 500 Kilometers
January Temperature Trend (C Deg / Year) (Various POR 1932-2002) January Precipitation Trend (mm / Year) (POR 1932-2002) + 0.023 + 0.058 0 125 250 500 Kilometers 0 125 250 500 Kilometers
August Temperature Trend (C Deg / Year) (Various POR 1932-2002) August Precipitation Trend (mm / Year) (POR 1932-2002) -0.024-0.023 + 0.013-0.013-0.026-0.015-0.020-0.016-0.017-0.022 + 0.772-0.013-0.017-0.015-0.017-0.011 + 0.010-0.030 + 0.031 + 0.016 0 125 250 500 Kilometers 0 125 250 500 Kilometers
Comments on Precipitation Trends Mixed signal in temperature. Eastern areas cooling in summer and fall Western areas show greatest rates of warming in spring. Large warming trend in Rio Grande Valley winter. Annual trend more cooling than warming but distinct spatial pattern.
Comments on Precipitation Trends Only seasonal trend identified is in fall with increase in pcp. in eastern and central area. No other seasons show trends. Annual trend mirrors fall season trend October positive trends dominate. Only two stations show month with negative trend.
Comments on Evaporation Trends Panhandle region dominated by increased evaporation in all seasons. Far west and Rio Grande Valley shows decreasing trend. Winters show more evaporation spatially while summer pattern more mixed.
Conclusions Results (kind of) track with NAST report of 2001. Some warming is occurring but most likely at low-end of early model scenarios. Eastern cooling trend anomaly. Precipitation more problematic and drying not shown in panhandle. Evaporation matches well with model ppt.
Future Work Examine trends and changes in rain days and rainfall intensity. Examine trends in humidity (mixing ratio). Correct evaporation data for land use/irrigation use? Potential sea surface temperature contribution?
Acknowledgements US Environmental Protection Agency for grant funding. Becky Brown, Sayali Gokhale, and Susan Street of TX State for assistance in data processing and mapping. Texas Water Development Board NOAA/National Climatic Data Center Legions of weather observers
Questions?