SUMMARY 



Precipitation from the Nueces River watershed was analyzed for recent trends. Of particular interest were 

 comparisons of precipitation across the three periods, 1940-57, 1958-81, and 1982-99, selected for study in the 

 potential long-term effects of the Rincon Project (Irlbeck and Ward 2000). Tropical cyclone occurrences in the 

 Adantic basin and possible relationships with ENSO and climate variables were investigated. An analysis was 

 conducted of Nueces River watershed precipitation anomalies stratified by ENSO type, to assess whether 

 ENSO may affect watershed precipitation. A multivariate comparison was conducted of daily precipitation 

 sampling distributions for the Rincon three study periods using data from the Corpus Christi WSO AP gauge. 

 Differences could point to more potential inundations of the Nueces delta marsh, despite possible similar 

 annual precipitation amounts. 



Precipitation analyses indicated highest amounts occiorred along the Nueces Bay coastline of the Rincon Project 

 study area. Least amounts occurred in the west-central area of the watershed. Precipitation from three gauges 

 located across the watershed displayed the same general pattern across the three study periods: least annual 

 amounts during the 1950s' drought, highest amounts during 1958-81 (second study period), and intermediate 

 amounts during 1982-99. Using a base period that included the 1950s, annual precipitation portrayed an 

 increasing trend. However, a broader time view using a base period that consisted of pre-1950s data produced 

 no particular trend in Nueces River watershed precipitation. 



The survey of studies of ENSO and some climate variables, and their possible relationships to tropical cyclone 

 activity in the Adantic basin jrielded results of analyses of interannual trends and multi-decadal variability. The 

 studies found that only weak Unear trends can be ascribed to the hurricane activity and that multi-decadal 

 variation is the stronger characteristic present (in particular; Gray, 1979, 1984; Gray et al, 1993; Landsea, 1993; 

 Landsea et al, 1992, 1999). Various environmental factors including are analyzed for interannual links to the 

 Adantic hurricane activity. Environmental variables showing significant, concurrent relationships to the 

 firequency, intensity and duration of Adantic hurricanes include the stratospheric Quasi-Biennial Oscillation, 

 Adantic sea surface temperatures, 200mb zonal winds, Caribbean sea level pressures, African West Sahel 

 rainfall, and ENSO. ENSO was linked to changes in tropical cyclone-caused damages. More damage occurred 

 during La Nina years followed by baseline years and El Nino years. 



ENSO related precipitation anomalies in the Nueces River watershed were investigated using monthly data 

 stratified by ENSO phase to develop proportion of months of record with precipitation that equaled or 

 exceeded a benchmark determined from the baseline years. Analyses were separately conducted for three 

 gauges of the Nueces River watershed. Results were variable and did not definitively point to either phase 

 expressing a consistent anomaly sense (positive or negative). Suggestions in the results include that two of 

 three gauges yielded more positive anomalies in La Nina months (eight tropical cyclones) than was obtained for 

 El Nino months (four tropical cyclones). Four of six anomalies were negative. Overall, the results suggest that 

 high variability in the watershed precipitation can mask whatever ENSO effects occur. Perhaps data for more 

 watershed gauges would be more revealing. 



The sampling distribution of Corpus Christi WSO AP daily precipitation was investigated per each Rincon 

 Project study period. While annual precipitation changed Utde after the 1 950s drought, possibly the distribution 

 of daily amounts differed from one Rincon study period to another. Differing distribution could favor more 

 marsh intmdations in some study period. Multivariate analysis was used to compare the sampling distributions 

 of the three study periods. Exploratory analyses revealed that the precipitation distribution of the first study 

 period that included the 1950s drought differed from each of the other two study periods. The second period 

 data did not differ from the third period data, suggesting that neither period would on average be dominant in 

 potential natural inundations of the Nueces delta marsh. 



The crosstabulated Corpus Christi WSO AP data revealed 21 (40 percent) of 52 years (since 1948) with large 

 precipitation events (=> 4 inches per day): 6 were El Nino years, 8 were La Nina years and 7 were baseline 

 years. Tropical cj'clones occurred in seven high-event years: five were La Niiia years and two were baseline 

 years. Annual precipitation exceeded 40 inches in 7 years of which 5 years were baseline years, 1 year was La 

 Nina, and 1 year was El Niiio and the greatest amount (48.07 inches) of the record. Of the seven high-annual 

 years, two years did not have a high daily-amount event. 



Appendix D ♦ D-11 



