Description
Current irrigation code uses a simple bucket model for hydrology but assumes the same size "bucket" everywhere and the same tolerance to water stress for every crop.
Proposed Solution
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Use site-specific soils information (e.g. from soils.nc files) to set soil saturation and maximum soil depth, initially using means but ideally ensembled (with ensemble IDs matching soil ensembles being assigned to model runs)
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Use crop identity to set crop-specific rooting depth and minimum water tolerance. Crop specific irrigation recommendations (e.g., management allowable depletion, MAD) should be available from CIMIS (e.g., https://cimis.water.ca.gov/Content/pdf/Irrigation_Scheduling_Using_CIMIS.pdf). The current test value (allowing SM to drop to 15% of WHC) looks too low relative to what I'm reading in CIMIS, which suggests a number around 50-60% WHC (40-50% MAD) for sensitive crops and 20% minWHC (80% MAD) for deeply rooted perennials on ideal soils. As an initial starting point for defaults I'd recommend we set ~25% minWHC for woody PFTs and 50% minWHC for annuals. Maybe something in between for irrigated pasture and other non-woody perennials.
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Use soil saturation and min(rootingDepth,max soil depth) to set overall water holding capacity (WHC)
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Finally, the irrigation management allows the specification of whether irrigation is done above or below canopy. For California this info should be in the harmonized LandIQ. When applying irrigation above canopy we also need to add a correction factor for canopy interception and direct evaporation.
Additional Context
#3762
Description
Current irrigation code uses a simple bucket model for hydrology but assumes the same size "bucket" everywhere and the same tolerance to water stress for every crop.
Proposed Solution
Use site-specific soils information (e.g. from soils.nc files) to set soil saturation and maximum soil depth, initially using means but ideally ensembled (with ensemble IDs matching soil ensembles being assigned to model runs)
Use crop identity to set crop-specific rooting depth and minimum water tolerance. Crop specific irrigation recommendations (e.g., management allowable depletion, MAD) should be available from CIMIS (e.g., https://cimis.water.ca.gov/Content/pdf/Irrigation_Scheduling_Using_CIMIS.pdf). The current test value (allowing SM to drop to 15% of WHC) looks too low relative to what I'm reading in CIMIS, which suggests a number around 50-60% WHC (40-50% MAD) for sensitive crops and 20% minWHC (80% MAD) for deeply rooted perennials on ideal soils. As an initial starting point for defaults I'd recommend we set ~25% minWHC for woody PFTs and 50% minWHC for annuals. Maybe something in between for irrigated pasture and other non-woody perennials.
Use soil saturation and min(rootingDepth,max soil depth) to set overall water holding capacity (WHC)
Finally, the irrigation management allows the specification of whether irrigation is done above or below canopy. For California this info should be in the harmonized LandIQ. When applying irrigation above canopy we also need to add a correction factor for canopy interception and direct evaporation.
Additional Context
#3762