and its maps have long been criticized as out of date and underestimating actual flood risk. Though floodplains are defined by the Federal Emergency Management Agency, the agency does not map every inch of the U.S. The Lower Rio Grande region, which spans much of Texas’ southern border and includes the Rio Grande Valley, is next with about 1 million people at risk. The San Jacinto region, which includes Harris County and Galveston, has the most people living in a floodplain: almost 2.5 million people are in a 100- or 500-year floodplain. The analysis identified how many buildings, homes, people, hospitals, roads and agricultural areas are in a floodplain. Reem Zoun, director of flood planning at the TWDB, said that to decide how to prevent flooding in Texas, the agency first needed to identify which areas of the state were at the most risk. Between 20, rising sea levels caused the Texas coastline to retreat about 4 feet per year on average, according to a 2021 University of Texas Bureau of Economic Geology report for the Texas General Land Office. Almost 50 inches of rain fell in some areas of Houston during Harvey - the highest rainfall amount in a single storm for any place in the continental U.S.Īt the same time, higher global temperatures are melting glaciers, increasing sea levels around the world - including in Texas - and making coastlines more vulnerable to storm surges. Heavier precipitation linked to climate change likely increased Hurricane Harvey’s total rainfall by as much as 19%, one study found. “I know it’ll truly go so far to save lives and people’s homes,” Paup said.Īs climate change worsens, higher global temperatures increase the amount of moisture in the air and thus the risk of extreme rainfall events, the Texas state climatologist and a national climate assessment have found. Each region is built around one of the state’s major watersheds. “Getting this program up and running is a really big deal,” TWDB Chair Brooke Paup said before the board approved the 15 regional plans, a major step in creating the statewide flood plan. The first projects proposed in the plan add up to $38 billion, including the massive coastal barrier proposal with its “Ike Dike,” a huge gate system proposed for the mouth of Galveston Bay. It will likely cost Texas tens of billions of dollars to protect people and property from floods. One-fifth of the state’s land - roughly 56,000 square miles - now fall within the 100-year floodplain, TWDB staff said in a presentation this week. Another 3.5 million people live in areas with a 0.2% chance of flooding each year, known as the 500-year floodplain. More than 2.4 million Texans live in areas that have a 1% chance of flooding each year, known as the 100-year floodplain, the analysis found. Flood risks in Texas are increasing as climate change brings heavier precipitation, stronger hurricanes and sea level rise and as the state’s population continues to climb. The analysis is part of the Texas Water Development Board’s first statewide flood plan, still in development, which the Legislature required in a 2019 law passed in response to Hurricane Harvey. ![]() USGS Home Water Climate Change Core Science Ecosystems Energy and Minerals Env.Sign up for The Brief, The Texas Tribune’s daily newsletter that keeps readers up to speed on the most essential Texas news.Īlmost 6 million Texans, or about 20% of the population, live in an area susceptible to flooding, according to first-of-its-kind data gathered as part of a statewide effort to harden Texas against floods and rising sea levels. Use our Water Science rainfall calculator to see how many gallons of water falls from the sky during a rainstorm. Map of streamgages where the water level is currently at or above flood stage or at high flow.Īll the water in floods comes from the sky-but have you ever wondered just how many gallons of water falls on an area when it rains? You might be surprised at how much water comes down. ![]() ![]() The most complete depiction of streamgages at or above flood stage is on the NWS River Conditions Map. Flood conditions may be more extensive than shown because the National Weather Service (NWS) has not identified a flood stage at all USGS streamgaging sites. The map below, (from USGS's WaterWatch Web site), shows the location of streamgages where the water level is currently at or above flood stage (depicted as a black triangle) or at high flow (depicted as blue circles) The high flow conditions are expressed as percentiles that compare the current (i.e., within the past several hours) instantaneous flow value to historical daily mean flow values for all days of the year.
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