Soil erosion matters because it degrades land quality, reduces agricultural productivity, and threatens water and ecosystem health. When soil is lost, the remaining soil becomes less fertile, making it harder for crops to grow and increasing the need for costly fertilizers and management techniques.

The main causes of soil erosion on U.S. farms are water runoff, wind, and intensive farming methods such as tillage and lack of crop cover. When rain falls on bare or poorly protected soil, it can wash away topsoil, especially on slopes or fields without conservation practices. Additionally, wind erosion can be significant in flat, exposed areas, particularly in the western U.S. and during droughts.

The Daily Erosion Project is a research initiative that estimates water runoff and soil erosion at the hillslope level, across U.S. farmlands each day using rainfall, soil, and land cover data. It provides publicly accessible maps and summaries to help farmers, researchers, and conservation agencies monitor erosion risk and evaluate management practices. The project supports decision-making by showing how much soil is being lost and where it is most vulnerable to erosion.

WEPP, or the Water Erosion Prediction Project, is a computer model used to estimate soil erosion and sediment delivery from agricultural, rangeland, and forested areas. It helps predict how different land uses, soil types, and weather conditions affect erosion rates, guiding conservation planning and management. When rainfall occurs, the planted crop and soil characteristics are used to determine if surface runoff will occur; then the program calculates estimated sheet, rill, and channel soil erosion, detachment, and deposition. Researchers and land managers use WEPP to assess the effectiveness of practices like terracing, cover crops, and buffer strips.

1. Precipitation is defined as the liquid equivalent (snow is melted) depth of water spatially averaged over the HUC12.
2. Runoff is defined as the amount of water leaving the DEP modelled hillslopes, averaged for a HUC12.
3. Detachment is defined as the amount of soil disturbed from the DEP modelled hillslope, averaged for a HUC12.
4. Hillslope Soil Delivery is defined as the amount of soil delivered to the bottom of the modelled hillslope, averaged for a HUC12.

A watershed is land where all water from rain or snow flows downhill to a common point, like a stream, river, or lake. It acts like a huge funnel, gathering water and moving it through connected creeks and rivers until it reaches a larger body of water. Every farm, city, or forest is part of a watershed, and how water moves through that area affects soil, water quality, and ecosystems.

HUC stands for Hydrologic Unit Code, a system used by the U.S. Geological Survey (USGS) to categorize and divide watersheds across the United States. Each watershed receives a unique code, ranging from 2 to 12 digits, that indicates its position within the overall drainage network, from large river basins to smaller subwatersheds. HUCs are commonly used in water resource management, environmental monitoring, and conservation efforts. The Daily Erosion Project uses 12-digit HUCs, which represent the most detailed level of watershed units in the hierarchy. 

Currently, the Daily Erosion Project covers selected states, primarily in the Midwest, including Iowa, Nebraska, Minnesota, and parts of Illinois, Missouri, Kansas, and Wisconsin. Expansion efforts are ongoing. 

Updated November 2025

As of November 2025, DEP makes just under one million WEPP model runs each day. The WEPP model itself is a single threaded job, but thankfully only takes a second to run for the 18+ years we are simulating. Even at a one-second execution time, having one million runs means that we have to implement some sort of parallel execution to have all the runs complete within a day (only ~100k seconds in a day!). 

DEP's goal is to have daily output from the previous day by approximately 6 AM of the current day. This represents a maximum time window of about six hours to accomplish the following tasks:  

• Update input climate files with yesterday's data
• Run the WEPP model one million times
• Process the WEPP output files and create summaries within the database 

As of this writing, the DEP processing is done on a Dell PowerEdge R840 with 4 physical processors (192 threads) and two mirrored 2 TB NVMe drives. These assets permit the DEP execution to complete by about 5 AM each morning. Ironically, the most computationally "expensive" component of this processing is the input-output associated with the numerous and small ASCII files used by the WEPP model. The NVMe drives allow these small operations to complete with limited latency. 

The parallelization happens with a programming script that launches multiple instances of WEPP at the same time. This Python code uses the standard library multiprocessing to proctor the runs. Again, the NVMe drives really make this possible as the multiple jobs are not stuck in I/O wait. 

The Daily Erosion Project (DEP) uses a tested and proven soil erosion model (the Water Erosion Prediction Project model or WEPP) that estimates soil erosion and water runoff occurring on hillslopes.  Estimates are based on hillslope conditions: for example, slope steepness, slope length, tillage used and crop growing in each field, soil type, and rainfall.  The conditions on each hillslope are identified from remote sensing: lidar for topography, satellite imagery for soil and crop management and field boundaries, NEXRAD radar for precipitation, and electronic databases for details such as soil type.  Sheet and rill soil erosion estimates are made for approximately one million randomly selected hillslopes in Iowa, with a similar density of hillslope erosion estimates occurring across all of the DEP coverage area.  From these DEP erosion estimates, we post daily the average hillslope soil loss (and water runoff) occurring for each HUC12 watershed in the DEP coverage area.  

Several technological tools assist in monitoring soil erosion, including remote sensing, GIS mapping, and erosion prediction models like WEPP. Satellite imagery and aerial photography are commonly used to observe vegetation cover and land use changes that influence erosion risk. Ground-based sensors and rainfall-runoff monitoring stations also deliver real-time data, while tools such as the Daily Erosion Project integrate these data sources for daily estimates across large landscapes.

The most effective erosion control practices for small farms include cover cropping and crop residue management, which protect soil surfaces from raindrop impact and decrease runoff velocity. Contour farming and terracing slow water movement downslope, trapping sediment and permitting it to infiltrate, while also decreasing the distance water travels. Buffer strips planted along field edges and waterways trap eroded sediment before it reaches streams, improving water quality and creating habitat benefits.

Soil loss decreases agricultural productivity by removing nutrient-rich topsoil, which forces farmers to use more fertilizers and drives up costs over time. Eroded fields become less able to retain water and nutrients, making crops more susceptible to drought and yield fluctuations. Over time, severe soil degradation can make land unusable for farming, risking food security and leading to the abandonment of once-productive agricultural land.

Communities can work together through watershed-based planning, where neighboring farmers, local agencies, and conservation groups coordinate erosion management strategies at a landscape scale rather than on individual fields. Voluntary conservation programs and incentives, such as cost-sharing for buffer strips, cover crops, or terracing, motivate farmers to adopt erosion control practices while building local expertise and peer support. Education and data sharing, including tools like the Daily Erosion Project, which display real-time erosion risks, help communities identify high-priority areas and collaboratively invest in the most effective practices for shared water resources and soil health.

Deforestation removes trees and vegetation that anchor soil with their roots, significantly increasing erosion as exposed soil gets washed away by rain and wind. Converting forests or grasslands into farms or cities removes surface plants, reducing soil absorption and increasing runoff, which accelerates erosion much more than in untouched areas. These land changes accumulate over time. Eroded slopes turn into gullies, sediment clogs waterways, and ecosystems break down, making restoration more challenging and costly.

Eroded sediment blocks rivers and lakes, reducing water clarity and increasing turbidity, which prevents sunlight from reaching aquatic plants and harms fish spawning areas. Sediment also carries pollutants like nutrients, pesticides, and heavy metals, which build up in water bodies and can cause harmful algal blooms and dead zones that suffocate aquatic life. The buildup of sediment decreases water storage capacity in reservoirs and raises water treatment costs for communities that depend on these water sources for drinking and irrigation.

Yes! Contact Laura Frescoln at frescoln@iastate.edu, to arrange a presentation.

The Daily Erosion Project offers hands-on training for undergraduate and graduate students who are serious about agricultural conservation and GIS technologies. If you're interested in applying your GIS, programming, or conservation skills to real-world watershed challenges, please contact Brian Gelder (bkgelder@iastate.edu) or Claudette Sandoval-Green (claudenm@iastate.edu) to learn about current opportunities and next steps.