Glossary

What the terms and units on this site mean, in plain words.

7DADM (7-day average of the daily maximum): The highest temperature each day, averaged over seven days. It is the usual measure of heat stress for fish, because it captures how hot the water gets each afternoon and not only the daily average.
Acequia (community ditch): A community-run irrigation system, and a form of local self-government: the people who hold water rights on the ditch govern it themselves. Each acequia elects a mayordomo, who runs the ditch and shares out its water, and commissioners (comisionados), who hold the membership meetings and manage its governance and finances. The families and individuals with rights to its water are called parciantes. Under New Mexico law, acequias are political subdivisions of the state.; Many acequias have existed since the Spanish colonial period, and for centuries they were the main local government for sharing surface water. They remain an important center of community and cultural life: neighbors clean the ditch together each spring (la saca de la acequia), and ditches along the same stream share water by long-standing custom. New Mexico has roughly 700 acequias.
Acre-foot: The amount of water that would cover one acre of land one foot deep: 325,851 gallons (43,560 cubic feet). It is the usual unit for the water held in a reservoir and for the volume a river carries over weeks or months.
Capacity and percent full: Capacity is the most a reservoir can hold at its normal full level. Percent full is the water held divided by that capacity. When we give one percent for a group of reservoirs, we add up the water and add up the capacity first, so a large reservoir counts for more than a small one.; Capacity is not fixed: sediment fills reservoirs, and operators revise their measurements. Each reservoir page says how well its capacity is known.
cfs (cubic feet per second): How fast water is flowing past a point: one cubic foot every second. A river running at 1 cfs for a whole day carries about 1.98 acre-feet.
Drought index (DSCI, Drought Severity and Coverage Index): A single number from 0 to 500 that the U.S. Drought Monitor uses to sum up drought across an area. It adds together the percent of the area at each drought level (D0 to D4), so 0 means no part of the area is abnormally dry and 500 means all of it is in exceptional drought. The home and Climate pages describe the share of the state in drought instead; the index is on the Drought page.
Drought levels (D0 to D4): The U.S. Drought Monitor sorts every area into steps: D0 abnormally dry, D1 moderate drought, D2 severe drought, D3 extreme drought and D4 exceptional drought. The levels are counted cumulatively, so "in severe drought or worse" means D2, D3 and D4 together.; The Monitor's map is a weekly judgment by experts who weigh many measurements. It is not a single reading.
Flood-control dam: A dam built mainly to hold back flood water. Some keep a small lake for recreation and leave a much larger space empty to catch floods, so their percent full is measured against that small conservation pool. Others, called dry dams, hold water only during a flood, so a reading of zero is normal.
Flow at the state line: The water carried out of New Mexico by its five largest exiting rivers: the Rio Grande, Pecos, Canadian, San Juan and Gila. We add up the readings of one gauge on each river, close to where it leaves the state, though not always at the border itself. Dams and diversions upstream shape what passes those gauges, and this is not the state's total outflow.
Median: The middle value: half of the past values were lower and half were higher. The "usual amount" on the home page is the median for the same days in 1991–2020, except for rain, which is compared with the average.
Much below normal to much above normal (the five ratings): The same five ratings are used for rivers, reservoirs, rain and temperature. They come from the percentile of a reading: below the 10th is much below normal, the 10th to the 24th is below normal, the 25th to the 75th is normal, the 76th to the 90th is above normal, and the 91st and above is much above normal. For temperature the words are colder and warmer.; Every rating is also written in words, never shown by color alone.
Normal: What is typical for the same time of year. We compare each reading with the same dates in 1991–2020, a 30-year span used as the standard for climate normals. Where a river gauge does not have enough years in that span, we use its whole record (at least 10 years) and say so.; For rivers, reservoirs and snow, normal is the middle range of what has happened before (the median), not an average or an expectation. Rain is the exception: its normal is the 30-year average, the standard climate normal, because in a dry season most years have almost no rain in a given week and a middle value would be close to zero. Some years are always above or below normal.
Percent of normal: A reading divided by the normal for the same dates, times 100. 100% is typical, 50% is half as much and 300% is three times as much. A short period with little in the normal, such as a week of rain in the dry season, can give a very large percent from a modest amount of water, so we show the amount too.
Percentile: A rank among past values. The 90th percentile means that 90 out of 100 past values for the same dates were lower. We rank each reading among the values for the same time of year in 1991–2020. Drought is ranked among the same weeks of 2000–2025, because the Drought Monitor's record is shorter.
PRISM: A climate model from Oregon State University's PRISM Climate Group that estimates rain and air temperature across the country on a grid, using weather-station readings and the shape of the land. We average it over each watershed and over the state. It is an estimate, not a reading at your location.
Provisional data: Recent readings from the U.S. Geological Survey and the Bureau of Reclamation are marked provisional, which means they may be corrected later. We show them as reported.
River section (stretch): We divide each river into sections, one for each watershed it flows through. A section's rating is the median of the percentiles of the gauges on it that week.
SNODAS: A snow model run by the National Weather Service's National Operational Hydrologic Remote Sensing Center. It estimates snow cover and the water in the snow every day on a grid of 1-kilometer squares. We average it over the state or a watershed. It is a model estimate, and we check it against measurements at snow stations.
Snow water equivalent (SWE, water in the snow): The depth of water you would get if the snow melted. It is not the depth of the snow: fresh snow is often about ten times as deep as the water in it, though the ratio varies a lot. We report inches of water because that is what matters for rivers and reservoirs.
Specific conductance (µS/cm, microsiemens per centimeter): How well water carries an electric current, which rises with the amount of dissolved salts. It is a quick way to tell how salty a river is: the higher the number, the saltier the water.
Storage reservoir: A reservoir that holds water for later release. The percent full on the home and Reservoirs pages counts the eight storage reservoirs with a known capacity: Heron, El Vado, Nambe Falls, Elephant Butte, Caballo, Eagle Nest, Avalon and Navajo.
Stream gauge: A station on a river that measures the water level and works out the flow from it. Most of our river numbers come from gauges run by the U.S. Geological Survey, the Bureau of Reclamation and the State of Colorado.
Water year: The year used for water totals, running from October 1 to September 30 and named for the year it ends in. It starts when the snow begins to build, so a winter and the runoff it feeds fall in the same year.
Watershed (HUC8): The land whose rain and snowmelt drain to one river or group of streams. The U.S. Geological Survey divides the country into watersheds with 8-digit codes, called HUC8s. We use them to divide rivers into sections and to show rain: 71 of them cover New Mexico.

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