Changes in precipitation patterns in Houston, Texas

Abstract There has been an alarming increase in the frequency of major flooding events along the Gulf Coast over the last three decades, primarily due to events of unprecedented, or extreme, rainfall. Using data from 63 rain gauges maintained by the Harris County Flood Control District's Flood Warning System (HCFCD FWS), this study examines the changes in daily precipitation amounts in the highly urbanized city of Houston, Texas, USA. The potential shift in annual precipitation patterns over a period of three decades (1989-2018) was examined by investigating the numbers of dry and wet days as well as annual precipitation totals over the study period. Wet days were then further scrutinized based on daily rainfall amounts (e.g., R10, R20, R30, R40, R50, R100) to determine if extreme events are beginning to dominate annual rainfall amounts. Trends were analyzed for statistical significance temporally using the Mann-Kendall and Sen's slope methods and for spatial trends using GIS applications. The results indicate a statistically significant increase in extreme rainfall at the expense of light, moderate, and heavy rainfall over time. The only negative relationship is found in dry days. The most statistically significant trends exist in the 99th percentile, maximum, and R100 parameters with p-values of 0.07, 0.08, and 0.11, respectively. There has been rapid growth and intensive development in the Houston area in recent decades that continues to this day, and land cover change has been significant as 12.6% of Harris County changed to one of four National Land Cover Database (NLCD) Urban classes (e.g., developed: barren, low intensity, medium intensity, high intensity). This confirms that urbanization has continued to increase while total vegetative and wetland coverage has decreased. The findings of this study provide essential guidance for city and state planners and engineers.