Precipitation
Environmental Indicators:
Societal Indicators:
Disclaimer: This tool is best viewed in Chrome, Firefox, Microsoft Edge, and Safari browsers. It does not work with Internet Explorer.
The initial map shows the annual percent change in precipitation by climate division from 1900 to 2023.
Each of the above highlighted attributes can be changed in the grey sidebar to the left of the map. Click the Update Map button to refresh the map based on your selections.
Click a location on the map and scroll down to see how precipitation changes over time at that location. Click on the tabs to view trends and additional information. Click on the magnifying glass icon on the right side of the map to search for a location.
Precipitation over time (Left Graph) displays precipitation over time at the selected location and based on your selections in the grey sidebar above. The dashed line is the median precipitation from 1900–1970.
All precipitation over time (Right Graph) displays the the monthly, seasonal, and annual precipitation at the selected location.
Precipitation relative to 1900–1970 (Left Graph) displays the percent of precipitation relative to the median precipitation from 1900–1970 at the selected location.
Is there a trend in precipitation over time? (Right Graph) displays the trend analysis (Mann Kendall and Sen Slope) for the selected location. Selecting All Trends from Selected Start Year shows trends from the start year through each following decade.
Over which time periods were there significant trends? displays the slope (wetter is positive and drier is negative) and p-value (significance) for different time periods with 30+ years of data. This shows how consistent changes in precipitation have been over time and helps compensate for when a time period began or ended during an extremely dry or wet period. Highlighted cells are for the selected start year (row).
Slope (In/yr):
| Slope ≥ 0.01 | -0.01 < Slope < 0.01 | Slope ≤ -0.01 |
P-value:
| Pval > 0.10 | 0.05 < Pval ≤ 0.10 | Pval ≤ 0.05 |
Reservoir characteristics, such as storage volume and operations, are shaped by the initial characteristics of the river system at the time in which the reservoir was designed. Precipitation impacts the size of the reservoir, which is designed to redistribute water throughout a year and across many years. Reservoirs authorized for flood control are designed to handle large precipitation events that are likely to occur once every 100 to 200 years. Reservoirs authorized for water supply may not have as much rain as they need to provide reliable water supply. Global warming intensifies the earth's water cycle, meaning that while the same amount of rain may fall on average, there may be long periods without rain punctuated by intense, heavy rainfall. Precipitation is also impacted by atmospheric-oceanic cycles that influence the jet stream, oscillating between drier and wetter conditions. For example, El Niño-Southern Oscillation (ENSO) transitions every few years, while the Atlantic Multi-decadal Oscillation can alter conditions for decades.