| 05 Sep 2025
Development of historical maps of land use-land cover, crop type, nutrients, and irrigation across CONUS (1938–2020) at different spatial resolutions
Abstract. Land use-land cover, nutrient inputs from fertilizer and manure, and irrigation are primary anthropogenic drivers of ecosystem functioning and degradation. Historical datasets covering these drivers at various spatial resolutions are essential for analyzing changes in these drivers as well as for input to models that estimate ecosystem outcomes such as water quality and runoff. We describe a new dataset for the conterminous United States (CONUS) – the Harmonized Land Nutrient Irrigation Dataset (HLNID) – that leverages existing datasets both at the county-scale (e.g., Census of Agriculture) and higher resolution land change model outputs (e.g., FORE-SCE) and remotely-sensed products (e.g., NLCD, CDL) to produce annual land use-land cover (including crop type), fertilizer and manure nutrient mass (nitrogen and phosphorus), and irrigation extent for the years 1938–2020. The flexible method can provide data at a range of custom spatial resolutions but we present results at 48 and 250 arc-seconds. The dataset reveals specific changes such as the increase in corn and soybean (replacing small grains and pasture) in the northern Great Plains since the 1990s, the spatial concentration of manure production in certain regions such as the uplands of the Southern Seaboard, and the expansion of irrigation in regions such as the Prairie Gateway. The method can readily incorporate new raw input datasets (e.g., CDL) to create updated versions but is limited by current time lags in state fertilizer sales data reporting.
This manuscript presents the Harmonized Land Nutrient Irrigation Dataset (HLNID), providing annual maps of land use–land cover (including crop type), fertilizer and manure nutrients (N and P), and irrigation extent across CONUS for 1938–2020 at flexible spatial resolutions. The study integrates county-level Census of Agriculture (CoA) data with multiple remote sensing and model-derived products using a demand–allocation framework.
The dataset is clearly within the scope of Earth System Science Data. It provides long-term, harmonized, spatially explicit inputs that are highly relevant for ecosystem, hydrologic, and biogeochemical modeling. The workflow is transparent and technically sound.
I recommend minor revision. The requested changes primarily concern clarification of assumptions and improved transparency.
Major Comments
1. Clarification of Dataset Nature
The manuscript appropriately states that HLNID reflects foundational datasets (e.g., CoA and NLCD) rather than providing an independent reconstruction (Section 4.2). However, this distinction should be emphasized earlier in the Methods section. The current framing may lead readers to interpret HLNID as a fully independent historical reconstruction rather than a harmonized synthesis framework.
2. Limited Treatment of Uncertainty
Although data sources and workflow are well documented, structured discussion of uncertainty is limited. Key assumptions that introduce uncertainty include:
A full quantitative uncertainty analysis may be beyond scope, but I recommend expanding Section 4.3 to include:
This would improve transparency without requiring substantial additional analysis.
3. Pre-1938 Guidance for LSM Applications
Because many land surface models initialize simulations from 1850, the 1938 start year may limit direct compatibility. While the chosen temporal range is justified, it would be helpful to provide guidance for users requiring earlier spin-up.
Without requiring full reconstruction of 1850–1937, the authors could consider:
Clarifying this would improve usability for the land modeling community.