Bays and estuaries are bodies of water where freshwater and marine environments mix. The Bay’s ecosystem depends on freshwater flowing downstream from rivers, bayous, and creeks. The amount and timing of freshwater inflows are directly related to salinity, the availability of nutrients to fuel the food web, and the availability of sediment that supports Bay habitats.

On average, the Houston-Galveston region receives 40-50 inches of rainfall a year. However, the region experienced an extreme drought between 2010 and 2012, with extremely dry conditions in 2011. In 2015 and 2016, rainfall rates were again above average with major flood events in May and April of those years, respectively. 2017 rainfall rates set records due to Hurricane Harvey, and 2018 had even higher inflows.

In 2022, we released a new freshwater inflows grading system. It is clear that Galveston Bay wildlife is impacted by both low and high extreme flow events. Water use and climate variability can result in both extreme low flow and extreme high flow events in the same year. In order to capture that variability, and the threat to freshwater inflows in the region, the grades are now calculated for both low and high flow events, and grouped in three-years of monthly  data, compared to the period of record (1940-2020, the most recent year of data). The graphs below represent grades based on the frequency of very high and very low flow events, grouped in three-year intervals. For the 2018-2020 time period, the low flow events were a grade of A and the high flow events were a grade of D. Extremely high flow years (like 2015-2017) received a F grade for high flow, and a grade of A for low flow. The last major Texas drought (2010-2013), led to low-flow grades of D and B for 2009-2011 and 2012-2014, respectively.  The historic drought years of 1950-1957 received low-flow freshwater inflow grades D, F and F for 1949-1951, 1952-1954, and 1955-1957.

Relative sea level rise is the combination of subsidence and rising ocean levels. Rising sea levels affect vital coastal habitats, as well as human communities. Galveston Bay’s long history of sea level rise, subsidence, storm surge, and flooding, makes sea level an issue of critical concern.

The grade for sea level rise continues to be an F. On average, sea level has risen two feet over the last 100 years at Pier 21 in Galveston and the trend is expected to continue. Coastal cities around the U.S. such as Miami Beach, Florida; Wilmington, Delaware and Annapolis, Maryland are already dealing with chronic coastal flooding and finding ways to adapt to become more resilient.

Winter water temperatures represent the lower range of temperatures that plants and animals endure in order to live in the Bay. As changes in climate impact water temperatures, species of plants and animals move into new areas where they were not previously found. The Bay’s winter water temperatures for December to February have increased for the first time to be ten percent higher than the average values of the previous 15 years, resulting in the grade being lowered from an A to a B. This could have implications for native species, invasive species, bacteria and oxygen levels in the bay.

Water acidity or alkalinity is measured by pH values. The lower the pH, the higher the acidity. Since Galveston Bay’s pH is determined by the mixing of saltwater from the Gulf of Mexico and freshwater from rivers and bayous in the watershed, changes in either source can have an impact. The pH values in the Bay are maintaining an appropriate range to support aquatic life, yielding the grade of an A