In 2024, the United States saw some 31.6 inches of precipitation. The main forms of precipitation include hail, drizzle, rain, sleet, and snow. Since the turn of the century, 2012 was the driest year on record with an annual precipitation of 27.5 inches. Regional disparities in rainfall Louisiana emerged as the wettest state in the U.S. in 2024, recording a staggering 71.25 inches (1.8 meters) of precipitation—nearly 14.4 inches (ca. 37 centimeters) above its historical average. In stark contrast, Nevada received only 9.53 inches (ca. 24 centimeters), underscoring the vast differences in rainfall across the nation. These extremes illustrate the uneven distribution of precipitation, with the southwestern states experiencing increasingly dry conditions that experts predict will worsen in the coming years. Drought concerns persist Drought remains a significant concern in many parts of the country. The Palmer Drought Severity Index (PDSI) for the contiguous United States stood at -3.39 in December 2024, indicating moderate to severe drought conditions. This reading follows three years of generally negative PDSI values, with the most extreme drought recorded in December 2023 at -3.93.

Typical annual rainfall data were summarized from monthly precipitation data and provided in millimeters (mm). The monthly climate data for global land areas were generated from a large network of weather stations by the WorldClim project. Precipitation and temperature data were collected from the weather stations and aggregated across a target temporal range of 1970-2000.

Weather station data (between 9,000 and 60,000 stations) were interpolated using thin-plate splines with covariates including elevation, distance to the coast, and MODIS-derived minimum and maximum land surface temperature. Spatial interpolation was first done in 23 regions of varying size depending on station density, instead of the common approach to use a single model for the entire world. The satellite imagery data were most useful in areas with low station density. The interpolation technique allowed WorldClim to produce high spatial resolution (approximately 1 km2) raster data sets.

In 2024, Louisiana recorded 71.25 inches of precipitation. This was the highest precipitation within the 48 contiguous U.S. states that year. On the other hand, Nevada was the driest state, with only 9.53 inches of precipitation recorded. Precipitation across the United States Not only did Louisiana record the largest precipitation volume in 2024, but it also registered the highest precipitation anomaly that year, around 14.36 inches above the 1901-2000 annual average. In fact, over the last decade, rainfall across the United States was generally higher than the average recorded for the 20th century. Meanwhile, the driest states were located in the country's southwestern region, an area which – according to experts – will become even drier and warmer in the future. How does global warming affect precipitation patterns? Rising temperatures on Earth lead to increased evaporation which – ultimately – results in more precipitation. Since 1900, the volume of precipitation in the United States has increased at an average rate of 0.20 inches per decade. Nevertheless, the effects of climate change on precipitation can vary depending on the location. For instance, climate change can alter wind patterns and ocean currents, causing certain areas to experience reduced precipitation. Furthermore, even if precipitation increases, it does not necessarily increase the water availability for human consumption, which might eventually lead to drought conditions.

Water is an essential ingredient to life on Earth. In its three phases (solid, liquid, and gas), water continuously cycles within the Earth and atmosphere to create significant parts of our planet’s climate system, such as clouds, rivers, vegetation, oceans, and glaciers. Precipitation is a part of the water cycle, where water particles fall from clouds in the form of rain, sleet, snow, ice crystals, or hail. So how does precipitation form? As water on Earth’s surface evaporates it changes from liquid to gas and rises into the atmosphere. Because air cools as altitude increases, the vapor rises to a point in the atmosphere where it cools enough to condense into liquid water or freeze into ice, which forms a cloud. Water vapor continues to condense and stick to other water droplets in the cloud until the weight of the accumulated water becomes too heavy for the cloud to hold. If the air in the cloud is above freezing (0 degrees Celsius or 32 degrees Fahrenheit), the water falls to the Earth as rain. If the air in the cloud is below freezing, ice crystals form and it snows if the air between the cloud and the ground stays below 0 degrees Celsius (32 degrees Fahrenheit). If a snowflake falls through a warmer part of a cloud, it can get coated in water, then refrozen multiple times as it circulates around the cloud. This forms heavy pellets of ice, called hail, that can fall from the sky at speeds estimated between 14 and 116 kmph (9 and 72 mph) depending on its size. A hailstone can range from the size of a pea (approximately 0.6 cm or 0.25 inches) to a golf ball (approximately 4.5 cm or 1.75 inches), and sometimes even reach the size of a softball (approximately 10 cm or 4 inches).Precipitation doesn’t fall in the same amounts throughout the world. The presence of mountains, global winds, and the unequal distribution of land and sea cause some parts of the world to receive greater amounts of precipitation compared with others. Areas with rising moist air generally indicate regions with high precipitation. According to the Köppen Climate Classification System, tropical wet and tropical monsoon climates receive annual precipitation of 150 cm (59 inches) or greater. Tropical wet regions, where rain occurs year-round, are found near the equator in central Africa, the Amazon rainforest, and southern India. Monsoons are storms with large patterns of wind and heavy rain that can span over a continent. Tropical monsoon climates are located mainly in Southeast Asia and areas around the Pacific Ocean, where annual rainfall is equal to or greater than areas with a tropical wet climate. Here, intense monsoon rains fall during the three hottest months of the year, which are usually between June and October. Snow and ice, which are most common in high altitudes and latitudes, cover most of the Earth’s polar regions. High altitude regions of the Andes, Tibetan Plateau, and the Rocky Mountains maintain some amount of snow cover year-round.Over the next century, it is predicted warming global temperatures will increase the temperature of the ocean and increase the speed of the water cycle. With a quicker rate of evaporation, there will be more water in the atmosphere, allowing clouds to produce heavier precipitation and more intense storms. Although storms would be more intense in wetter regions, increased evaporation could also lead to extreme drought in drier areas of the world. This would greatly affect farmers who grow crops in dry locations like Southern California or Kansas.This map layer shows Earth's mean precipitation (measured in centimeters per month) averaged from 1981 to 2012 as calculated but the Copernicus Climate Change Service. The data was collected from the Copernicus satellite and validated with precipitation measurements from weather stations. Scientists averaged all of the amounts (originally collected in meters) occurring each month together, and they calculated the average of each month over 30 years to create this map.

The North America climate data were derived from WorldClim, a set of global climate layers developed by the Museum of Vertebrate Zoology at the University of California, Berkeley, USA, in collaboration with The International Center for Tropical Agriculture and Rainforest CRC with support from NatureServe.The global climate data layers were generated through interpolation of average monthly climate data from weather stations across North America. The result is a 30-arc-second-resolution (1-Km) grid of mean temperature values. The North American data were clipped from the global data and reprojected to a Lambert Azimuthal Equal Area projection. Background information on the WorldClim database is available in: Very High-Resolution Interpolated Climate Surfaces for Global Land Areas; Hijmans, R.J., S.E. Cameron, J.L. Parra, P.G. Jones and A. Jarvis; International Journal of Climatology 25: 1965-1978; 2005.Files Download

[Metadata] Mean Annual Rainfall Isohyets in Millimeters for the Islands of Hawai‘i, Kaho‘olawe, Kaua‘i, Lāna‘i, Maui, Moloka‘i and O‘ahu. Source: 2011 Rainfall Atlas of Hawaii, https://www.hawaii.edu/climate-data-portal/rainfall-atlas. Note that Moloka‘I data/maps were updated in 2014. Please see Rainfall Atlas final report appendix for full method details: https://www.hawaii.edu/climate-data-portal/rainfall-atlas. Statewide GIS program staff downloaded data from UH Geography Department, Rainfall Atlas of Hawaii, February, 2019. Annual and monthly isohyets of mean rainfall were available for download. The statewide GIS program makes available only the annual layer. Both the monthly layers and the original annual layer are available from the Rainfall Atlas of Hawaii website, referenced above. Note: Contour attribute value represents the amount of annual rainfall, in millimeters, for that line/isohyet. For additional information, please see metadata at https://files.hawaii.gov/dbedt/op/gis/data/isohyets.pdf or contact Hawaii Statewide GIS Program, Office of Planning and Sustainable Development, State of Hawaii; PO Box 2359, Honolulu, Hi. 96804; (808) 587-2846; email: gis@hawaii.gov; Website: https://planning.hawaii.gov/gis.

Precipitation in Iraq increased to 191.01 mm in 2023 from 164.88 mm in 2022. This dataset includes a chart with historical data for Iraq Average Precipitation.

The average for 2020 based on 178 countries was 1168 mm per year. The highest value was in Colombia: 3240 mm per year and the lowest value was in Egypt: 18 mm per year. The indicator is available from 1961 to 2021. Below is a chart for all countries where data are available.

Average rainfall in Spain amounted to some 669.1 millimeters in 2024. This represents an increase in rainfall of over 24 percent in comparison to the previous year. During the period in consideration, Spain's wettest year was 2018, when the average precipitation reached a record high of 808 millimeters. Since then, rainfall in the Mediterranean country has mostly seen a continual annual decline until 2023.

The observed, historical data is produced by the Climatic Research Unit (CRU) of University of East Anglia. Data is presented at a 0.5º x 0.5º (50km x 50km) resolution. Data includes the average rainfall, minimum temperature, average temperature and maximum temperature in Vietnam from January to December in period of time 1901 - 2020. The data is presented on a 30 year interval. The unit of rainfall is mm and the temperature is Celsius degree.

The National Forest Climate Change Maps project was developed by the Rocky Mountain Research Station (RMRS) and the Office of Sustainability and Climate to meet the needs of national forest managers for information on projected climate changes at a scale relevant to decision making processes, including forest plans. The maps use state-of-the-art science and are available for every national forest in the contiguous United States with relevant data coverage. Currently, the map sets include variables related to precipitation, air temperature, snow (including snow residence time and April 1 snow water equivalent), and stream flow.Historical (1975-2005) and future (2071-2090) precipitation and temperature data for the contiguous United States are ensemble mean values across 20 global climate models from the CMIP5 experiment (https://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-11-00094.1), downscaled to a 4 km grid. For more information on the downscaling method and to access the data, please see Abatzoglou and Brown, 2012 (https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/joc.2312) and the Northwest Knowledge Network (https://climate.northwestknowledge.net/MACA/). We used the MACAv2- Metdata monthly dataset; monthly precipitation values (mm) were summed over the season of interest (annual, winter, or summer). Absolute and percent change were then calculated between the historical and future time periods.Raster data are also available for download from RMRS site (https://www.fs.usda.gov/rm/boise/AWAE/projects/NFS-regional-climate-change-maps/categories/us-raster-layers.html), along with pdf maps and detailed metadata (https://www.fs.usda.gov/rm/boise/AWAE/projects/NFS-regional-climate-change-maps/downloads/NationalForestClimateChangeMapsMetadata.pdf).

30-year Average precipitation represents the average amount (mm) of precipitation received in a month across a 30 year period (1961-1991, 1971-2000, 1981-2010, 1991-2020). These values are calculated across Canada in 10x10 km cells.

Annual rainfall is the total accumulated rain over one year. Rain is vital for life, including plant growth, drinking water, river ecosystem health, and sanitation. Floods and droughts affect our environment, economy, and recreational opportunities.

This dataset shows annual average rainfall across New Zealand for 1978 as part of the data series for years 1972 to 2013. Annual rainfall is estimated from the daily rainfall estimates of the Virtual Climate Station Network (NIWA).

This dataset relates to the "Annual average rainfall" measure on the Environmental Indicators, Te taiao Aotearoa website.

Geometry: grid Unit: mm/yr

In 2022, the annual rainfall in the Italian city of Naples was the highest among the biggest cities in Italy, at 84 centimeters. Milan and Turin accounted for over 30 centimeters, around half of their usual precipitation, considering that 2022 was the hottest year recorded since 1971. Rome also recorded the lowest precipitation since 2010.

Contained within the 3rd Edition (1957) of the Atlas of Canada is a plate that shows two maps for the annual total precipitation. Annual precipitation is defined as the sum of rainfall and the assumed water equivalent of snowfall for a given year. A specific gravity of 0.1 for freshly fallen snow is used, which means that ten inches (25.4 cm) of freshly fallen snow is assumed to be equal to one inch (2.54 cm) of rain. The mean annual total precipitation and snowfall maps on this plate are primarily based on thirty-year data during the period 1921 to 1950 inclusive.

Precipitation in Iran increased to 204.20 mm in 2023 from 183.75 mm in 2022. This dataset includes a chart with historical data for Iran Average Precipitation.

This metadata record describes the 30-year annual average of precipitation in millimeters (mm) and temperature (Celsius) during the period 1990–2019 for North America. The source data were produced by and acquired from DAYMET daily climate data (2020) and presented here as a series of two 1-kilometer resolution GeoTIFF files. An open source python code file used to process the data is also included.

Rainfall averages for UK over the 30-year 1961-1990, interpolated to a 1 km grid. This 30-year period is a Primary Reference Period recommended by World Meteorological Organisation.

Historical changes of annual temperature and precipitation indices at selected 210 U.S. cities

This dataset provide:

Annual average temperature, total precipitation, and temperature and precipitation extremes calculations for 210 U.S. cities.

Historical rates of changes in annual temperature, precipitation, and the selected temperature and precipitation extreme indices in the 210 U.S. cities.

Estimated thresholds (reference levels) for the calculations of annual extreme indices including warm and cold days, warm and cold nights, and precipitation amount from very wet days in the 210 cities.

Annual average of daily mean temperature, Tmax, and Tmin are included for annual average temperature calculations. Calculations were based on the compiled daily temperature and precipitation records at individual cities.

Temperature and precipitation extreme indices include: warmest daily Tmax and Tmin, coldest daily Tmax and Tmin , warm days and nights, cold days and nights, maximum 1-day precipitation, maximum consecutive 5-day precipitation, precipitation amounts from very wet days.

Number of missing daily Tmax, Tmin, and precipitation values are included for each city.

Rates of change were calculated using linear regression, with some climate indices applied with the Box-Cox transformation prior to the linear regression.

The historical observations from ACIS belong to Global Historical Climatological Network - daily (GHCN-D) datasets. The included stations were based on NRCC’s “ThreadEx” project, which combined daily temperature and precipitation extremes at 255 NOAA Local Climatological Locations, representing all large and medium size cities in U.S. (See Owen et al. (2006) Accessing NOAA Daily Temperature and Precipitation Extremes Based on Combined/Threaded Station Records).

Resources:

See included README file for more information.

Additional technical details and analyses can be found in: Lai, Y., & Dzombak, D. A. (2019). Use of historical data to assess regional climate change. Journal of climate, 32(14), 4299-4320. https://doi.org/10.1175/JCLI-D-18-0630.1

Other datasets from the same project can be accessed at: https://kilthub.cmu.edu/projects/Use_of_historical_data_to_assess_regional_climate_change/61538

ACIS database for historical observations: http://scacis.rcc-acis.org/

GHCN-D datasets can also be accessed at: https://www.ncei.noaa.gov/data/global-historical-climatology-network-daily/

Station information for each city can be accessed at: http://threadex.rcc-acis.org/

• 2024 August updated -

  Annual calculations for 2022 and 2023 were added.

  Linear regression results and thresholds for extremes were updated because of the addition of 2022 and 2023 data.

  Note that future updates may be infrequent.

• 2022 January updated -

  Annual calculations for 2021 were added.

  Linear regression results and thresholds for extremes were updated because of the addition of 2021 data.

• 2021 January updated -

  Annual calculations for 2020 were added.

  Linear regression results and thresholds for extremes were updated because of the addition of 2020 data.

• 2020 January updated -

  Annual calculations for 2019 were added.

  Linear regression results and thresholds for extremes were updated because of the addition of 2019 data.

  Thresholds for all 210 cities were combined into one single file – Thresholds.csv.

• 2019 June updated -

  Baltimore was updated with the 2018 data (previously version shows NA for 2018) and new ID to reflect the GCHN ID of Baltimore-Washington International AP. city_info file was updated accordingly.

  README file was updated to reflect the use of "wet days" index in this study. The 95% thresholds for calculation of wet days utilized all daily precipitation data from the reference period and can be different from the same index from some other studies, where only days with at least 1 mm of precipitation were utilized to calculate the thresholds. Thus the thresholds in this study can be lower than the ones that would've be calculated from the 95% percentiles from wet days (i.e., with at least 1 mm of precipitation).

Average Rainfall for the Months (June to September) from 2010 to 2019