|Drought Now Rated "Exceptional" for Some;
Still No Relief In Sight for Lower RGV
April 17th Update: Worst Conditions Cover Zapata and Jim Hogg County
Rainfall and Temperature: Extremely dry conditions continue across most of Deep South Texas and the lower Rio Grande Valley, particularly from Hidalgo and Brooks County westward to Jim Hogg, Starr, and Zapata Counties. Monthly rain aggregates were highest near the coast, including Kenedy, Willacy, and Cameron Counties, but even in these areas, only scattered locations received close to one quarter of an inch. Most significantly, no rain has fell since March 1st in many areas from Hidalgo and Brooks County westward. Where rain has fallen in these areas since February, totals have generally been a tenth of an inch or less, and a few locations have not see measurable rain since January. In the six months from October 2007 through March 2008, rainfall across the region has averaged 2 to 4 inches, which is 4 to 7 inches below normal. Virtually no rain has fallen since April 1st.
Drought Conditions: The combination of virtually no rainfall, prolonged above normal with bouts of record temperature, and nearly persistent moisture robbing winds, have allowed drought conditions to rapidly increase. A recent period of very dry and warm weather, especially across the western and northern portion of the Lower Rio Grande Valley, has resulted in the highest level of drought in these areas. According to the Regional Drought Monitor, exceptional drought conditions cover all of Zapata and Jim Hogg County, as well as northern Starr, and western Brooks County. The remainder of Brooks, as well as all of Hidalgo, and the western tips of Cameron and Willacy County, are in extreme drought. This includes portions of the more heavily populated Lower Rio Grande Valley, including McAllen, Pharr, and Weslaco. Severe drought covers the remainder of the area, including Brownsville, Harlingen, and Raymondville. These conditions are mainly affecting agricultural interests, including pastures and grasslands.
Agricultural Impacts: Needless to say, the worsening drought conditions continue to rapidly dry out near surface soils, and soil moisture across most of Deep South Texas and the Lower Rio Grande Valley is abnormally to excessively dry. According to the United States Department of Agriculture and the Texas A&M Agrilife Extension Service, the worsening drought is beginning to take a toll on crop and cattle alike. Dryland crops are increasingly stressed by the persistent winds and warm, dry weather. While citrus and vegetable harvests continue, many dryland producers halted planting of sorghum. Corn, cotton, onions, and other crops have progressed well under irrigation. Producers continue to provide supplemental feed to local cattle ranches due to the lack of fully developed spring forage. Daily evaporation rates continue to increase, now averaging nearly one half an inch.
Wildfire Danger: The combination of above normal temperatures, abundant dry fuels (a result of strong growth during the rainy 2007), repeated surges of very low humidity, and persistent winds, continue to maintain a moderate to high threat for wildfire development and growth. The latest Keetch-Byram Drought Index indicate high values above 600 across all of Deep South Texas, with values exceeding 700, or high to extreme, in all but Cameron and Willacy Counties. Burn bans remain in effect for all but Kenedy County, and residents are strongly urged to use extreme caution when disposing of lighted materials, and refrain from any outdoor burning activities.
Hydrologic Impacts: Water storage levels, while remaining fairly high, continue to decrease during this warm, dry spring. At Amistad Reservoir, storage has dropped to 84 percent of normal conservation; storage at Falcon Reservoir is now down to 45 percent. Water storage levels are expected to continue decreasing across the Lower Rio Grande Valley reservoirs in response to incresaing demands from municipalities, and the need for peak irrigation during the heart of the spring growing season. According to the State of Texas Commission on Environmental Quality, there are currently three public water systems in Hidalgo County under mild rationing.
Guidance from the Climate Prediction Center (CPC) indicates that the current moderate La Niña pattern in the tropical Pacific Ocean will persist through the rest of April. This will likely maintain a warm and dry weather pattern over Deep South Texas and the Lower Rio Grande Valley. After a brief break in the winds on the 18th, as well as some chance for some rain especially toward the coast, a return of hotter and dry weather, along with gusty winds in some areas, is expected from late in the weekend through at least the middle of next week. Temperatures near 100°F are possible between the 20th and 22nd across the hardest hit areas of Starr, Jim Hogg, and Zapata Counties. Significant and widespread soaking rainfall is not expected throughout the rest of April.
Longer range guidance from CPC indicates that the moderate La Niña pattern will likely continue throughout the rest of spring 2008. This persistent pattern will in turn maintain above normal temperatures and below normal rainfall for the region through June. As a result, severe to extreme drought conditions are expected to persist and perhaps intensify a bit further across Deep South Texas and the Lower Rio Grande Valley. However, CPC expects that the current La Niña pattern could weaken some as we move into the summer months. This weakening La Niña pattern may allow for somewhat increased rain chances by mid summer, which may provide some improvement of the current drought conditions affecting the region. However, near normal to above normal temperatures are expected to continue through June.
With aggregate rainfall forecasts to remain below average for the next several months, the potential for widespread spring flooding is virtually nil. That said, one must remain alert to localized slow moving or stationary thunderstorms as we move toward summer, and low level atmospheric moisture continues to increase. Such storms can produce very heavy amounts of rainfall in a short period of time, causing flash flooding of poor drainage areas, arroyos, and other prone locations.
Below are graphical data showing, from left: The April 15th Texas Drought Monitor; The latest April through June forecast temperature departures from average, and the latest April through June forecast precipitation departures from average. The Rio Grande Valley is inside the small box. Click each for a larger image.