The 2011 drought in Texas is widely acknowledged to be the state's worst one-year drought on record, but why is this so? The most immediate reason is that I, as Texas State Climatologist, am the de facto authority for such statements, and I declared it to be so. The rapid acceptance of this judgment by the popular press implies either a widespread gullibility on their part or a recognition that the statement at least partly reflects the reality of the situation. This talk describes the particular aspects of Texas climatology, agriculture, water storage and use, and 2011 weather events that lead to the judgment of "worst one-year drought on record".

From west to east, Texas has a widely-varying precipitation climatology. Most of the state normally experiences significant precipitation throughout the year, but with two particularly rainy seasons in late spring and early fall. The most negative precipitation minus evaporation numbers are found in summer, when very high temperatures coincide with a seasonal minimum in precipitation. Agriculturally, there are two seasons: the cool season, when winter wheat develops and cattle often need hay to supplement cool-season grass forage, and the warm season, when most other crops develop and warm-season grasses grow. Urban water demands are minimal during the cool season, so the cool season is a time of replenishment in preparation for drawdown during the warm season. These factors make spring and summer rains the most critical rains of the year for most of the state. The greatest potential crop impacts are felt during spring and early summer, while the greatest potential impacts on cattle and water utilities are felt during late summer. For these reasons, the one-year drought severity is assessed according to conditions during the summer, reflecting rainfall deficits that have built up during the preceding six to twelve months. By that measure, the 2011 drought is easily the worst statewide one-year drought on record, as measured by statewide accumulated precipitation during the months leading up to and including summer 2011. Furthermore, the one-year drought is the worst local drought in the past 100 years across more than half the state.