Texas has nearly hit the drought crossover point. Drought severity right now statewide is similar to severity a year ago at this time. Specifically:

The last time 10% of the state was not abnormally dry: February 15, 2011.

The last time only 81% of the state was in drought: March 8, 2011.

The last time only 56% of the state was in severe or worse drought: March 8, 2011.

The last time only 36% of the state was in extreme or worse drought: March 22, 2011.

The last time only 18% of the state was in exceptional drought: April 26, 2011.

We may see more improvement in the US Drought Monitor next week, as the full effects of this week’s rainstorm get tallied up. Meanwhile, with most Texans living in the eastern half of the state, it’s easy to forget that many parts of Texas are much worse off now than they were at this time last year.

The House Committee on Natural Resources held a hearing on Thursday on drought issues. This was my status report to them:

INTRODUCTION

La Nina, a coupled atmosphere-ocean weather pattern involving unusually cool temperatures in the tropical Pacific Ocean, has such a strong effect on jet streams and weather patterns that Texas wintertime precipitation is below normal four times out of five. Fortunately for much of Texas, this winter was one of the exceptional years.

Texas monthly rainfall was above normal in December, January, and February, following ten consecutive months of below-normal rainfall. March rainfall to date may already be sufficient to ensure a fourth consecutive above-normal month.

This welcome rainfall has not been distributed evenly across the state. While some parts of the state can now be considered to be out of drought, other parts remain in exceptional drought status.





REGIONAL SUMMARY

The figures at the end of this document embedded here provide an overview of conditions across the state.

Current drought status is indicated using the U.S. Drought Monitor. The latest update includes rainfall through Monday night, so the impact of the rainfall Tuesday and Wednesday is not yet shown. Most of Texas is designated “L”, meaning that longer-term drought issues, such as water supply, dominate. Other parts are designated “SL”, meaning that both short- and long-term drought impacts are being experienced.

The details of drought across Texas are depicted using two maps generated by the Office of the State Climatologist from high-resolution National Weather Service precipitation analyses. The first map shows rainfall compared to normal over the past 1-3 months, illustrating the wet winter experienced by most of the state. The second map shows rainfall compared to normal over the past 12-24 months, illustrating the extent to which the recent rains have made up for the longer-term precipitation deficits. Please note that there are some incorrect details in these maps due to radar biases that have not been entirely corrected. In particular, the details of the rainfall pattern in Texas east of I-45 are incorrect, and the overall amount of precipitation in South Texas is underestimated.

The Dallas-Fort Worth area is farthest from drought. DFW Airport has received 13.57″ of rain so far this year, almost twice normal. This region, unlike most other areas of the state, did not set a record for driest twelve consecutive months ever during the 2011 drought, so recovery came faster. However, because of the inability to transfer water from Lake Texoma, parts of the area are still highly vulnerable to drought.

East Texas was already in drought in 2010, so it has taken longer for the area to recover. Widespread rains have helped considerably. Major rivers are returning to normal base flows, and most major reservoirs are nearly at conservation storage capacity. Tyler has received 12.31″ of rain so far this year, nearly three inches above normal. Additional rainfall is still needed to produce full storage by summer, but conditions are much better than they were last year at this time.

Southeast Texas is also close to recovery from drought. IAH has received 17.66″ of rain so far this year, which is twice normal. As with East Texas, the last remaining step is for lake and groundwater levels to return to normal.

Central Texas is also doing very well. Rainfall so far this year at Austin-Bergstrom is 15.99″, which is two and a half times normal. Indeed, as lakes fill up and streamflows return to normal, the primary water issue for many agricultural interests is the lack of a break in the rainfall sufficient to prepare fields and plant crops.

The last region on the favorable side of the ledger is the cross-timbers region from west of Fort Worth through Abilene. Abilene itself has received 5.64″ so far this year, which is one and a half times normal, and some areas east and south of Abilene have received much more. The area is locally either free from drought or much improved.

The overall drought picture in this area, as well as much of central Texas, is complicated by the fact that the largest rivers flowing through the region are fed by rainfall farther upstream, and upstream rainfall has been lacking. Thus, local meteorological drought conditions may be excellent, but there may still be major reservoir storage issues due to lack of inflows from upstream.

San Angelo is a case in point. Rainfall there has been 7.13″, over twice normal for the year so far. Yet most major reservoirs in the area are very low. Upstream of San Angelo, rainfall totals are running near or below normal and have been inadequate to restore normal stream flows.

Across West Texas, from the Panhandle to Big Bend, drought conditions are still prevalent. Precipitation is normally relatively light during the wintertime, so even above-normal precipitation this time of year is generally insufficient to produce recovery from drought, and most places have not even received above-normal precipitation. Here are some year-to-date totals: Amarillo 1.24″, 60% of normal; Lubbock 1.19″, 60% of normal; Midland 1.30″, 80% of normal; El Paso 0.76″, 75% of normal. Dust storm activity has been high and is likely to remain high through the spring. On the bright side, there was so little vegetation growth last year that wildfires have not yet been a problem.

In South Texas, there has been some rain but not nearly enough to eliminate the drought. Corpus Christi, for example, has received 5.44″ of rain so far this year, only slightly above normal. The situation there is like a “dunked biscotti”: the top of the soil is soft and moist, but below the surface the ground remains dry and crunchy.

OUTLOOK FOR THE REST OF 2012

The outlook in the first paragraph is based primarily on forecasts from the Climate Prediction Center (CPC) branch of the National Weather Service. The current La Niña conditions in the Tropical Pacific Ocean are forecasted weaken to neutral conditions by the end of April. By May, not only will La Niña be gone, but so to goes our ability to forecast seasonal rainfall. Rainfall in May and June depends upon unforecastable details in how squall lines form and move, and summertime disorganized rainfall is notoriously unpredictable. CPC predicts a slightly enhanced change of above-normal temperatures across Texas and below-normal precipitation along the Gulf Coast. The summertime forecast also has slightly enhanced chances of above-normal temperatures. For next winter, not much information is available at this stage. More will become clear in mid-June when skillful forecasts of El Niño or La Niña conditions next winter will be possible.

The wide range of drought conditions presently seen across the state is likely to continue. For places with ample water supplies, the primary danger will be a sudden spell of intense dry weather, but even if such an event occurs it is unlikely to cause problems as large as those during the summer of 2011.

In most of West Texas, conditions remain dire. Reservoirs are mostly low or empty, and the topsoil has not become moist during the winter. If below-normal rainfall continues, agricultural losses could be as large or larger there than in 2011. Even if above-normal rainfall commences now, it may already be too late to produce substantial runoff to reservoirs in time for summer.

Between those two extremes, the situation is promising but precarious. Without deep soil moisture, the area will be vulnerable to an extended dry period that dries out the soil and makes water unavailable for plants. Tree mortality from last year and early springtime growth of grasses would also contribute to very high fire danger if things dry out. Yet if above-normal rain continues, especially during the climatologically wet months of May and June, the present lack of a backup deep soil water supply for roots may not matter.

In response to the precarious situation across much of Texas, a team of scientists and engineers at the University of Texas and Texas A&M University, including myself, coordinated by Prof. David Maidment of U.T., is working to apply research-quality modeling techniques to produce and make available to the State of Texas forecasts of soil moisture, streamflow, and reservoir levels. We are hopeful that some of the technology developed or refined in the state’s public universities can be utilized for the benefit of local, regional, and state decision-makers during this exceptional time.

CLOSING REMARKS

In 2011, the entire state of Texas experienced extreme drought conditions. In 2012, conditions will vary widely across the state, from extreme or exceptional drought conditions to no drought at all. This will complicate drought response. Much of the rain has fallen in heavily-populated areas of the state, so many Texans may forget that other parts of the state are suffering under drought impacts that may be as bad or worse locally as those in 2011.