Uncertainties in transpiration estimates

Area of Science:

• Hydrology
• Ecology
• Climate Science

Background:

• The relative contribution of plant transpiration versus evaporation from other sources (e.g., soil, water bodies, canopy interception) to global water cycling is a long-standing debate.
• Previous studies, including Jasechko et al. (2013), have proposed significant roles for transpiration in land evaporation.
• Accurate quantification is crucial for understanding land-atmosphere interactions and improving climate models.

Purpose of the Study:

• To critically evaluate the global transpiration ratio estimated by Jasechko et al. (2013).
• To reassess the contribution of plant transpiration to total land evaporation.
• To highlight the impact of data selection and uncertainty quantification on hydrological estimates.

Main Methods:

• Re-analysis of global evaporation data, considering alternative input datasets.
• Conservative accounting of uncertainties associated with hydrological measurements.
• Comparison of revised transpiration estimates with existing climate model outputs.

Main Results:

• The estimated global transpiration ratio is significantly reduced and widened to 35-80% when alternative data and conservative uncertainty assessments are applied.
• This revised range suggests a less dominant role for transpiration compared to the 80-90% initially proposed.
• The findings indicate potential discrepancies between observational data and climate model assumptions.

Conclusions:

• The global importance of plant transpiration requires further investigation with more comprehensive catchment-scale data.
• Reducing uncertainty in hydrological measurements is essential for reconciling observational data with climate model projections.
• Continued research is needed to refine our understanding of the global water cycle and land-atmosphere feedbacks.