the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 May 2022
Climate Response to Severe Forestation: A Regional Climate Model Intercomparison Study
Abstract. The biogeophysical effects of severe forestation are quantified using a new ensemble of regional climate simulations over North America and Europe. Following the protocol outlined for the Land-Use and Climate Across Scales (LUCAS) intercomparison project, two sets of simulations are compared, FOREST and GRASS, which respectively represent worlds where all vegetation is replaced by trees and grasses. Three regional regional models were run over North America. One of them, the Canadian Regional Climate Model (CRCM5), was also run over Europe in an attempt to bridge results with the original LUCAS ensemble, which was confined to Europe. Overall, the CRCM5 response to forestation reveals strong inter-continental similarities, including a pronounced wintertime and springtime warming concentrated over snow-masking evergreen forests. Crucially, these northern evergreen needleleaf forests populate lower, hence sunnier latitudes in North America. Snow masking reduces albedo similarly over both continents, but stronger insolation amplifies the net shortwave radiation and hence warming simulated over North America. In the summertime, CRCM5 produces a mixed forestation response, with warming over northern needleleaf forests and cooling over southern broadleaf forests. The partitioning of the turbulent heat fluxes plays a major role in determining this response, but it is not robust across models over North America. Implications for the inter-continental transferability of the original LUCAS results are discussed.
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RC1: 'Comment on egusphere-2022-291', Anonymous Referee #1, 25 May 2022
General Comment
This study uses three regional climate models, albeit two of them are very similar (CRCM5 and CRCM6), to assess the biogeophysical impacts of forestation in North America (NA). The methodology follows the protocol designed in the first phase of the CORDEX flagship pilot study Land Use and Climate Across Scales (LUCAS) and described in Davin et al. (2020). The study also contextualises its results for North America with those already published for Europe, and explores the transferability of results between the two continents. The work is well within the scope of the journal and provides a substantial contribution to the field.
Major Comments
- The title and abstract are a little misleading. This study does not present new results for Europe, nor is Europe its focus. This study focuses primarily on North American and contextualises these results in the framework of the CORDEX LUCAS work for Europe. The results for Europe have been presented previously in Davin et al (2020) and elsewhere, which is correctly referenced throughout the manuscript. In this regard, it is strongly recommended to (a) include North America in the manuscript’s title, and (b) revise some of the sentences in the abstract and introduction to show that the focus is North America.
- It would be beneficial to see a confirmation of the authors hypothesis that the difference between NA and Europe in winter is due to the presence of Evergreen Needleleaf forests and snow cover at lower latitudes in NA compared to Europe.
- It is important to compare the biogeophysical impacts in NA and Europe during spring in addition to the winter. In Europe, the snow albedo effect is strongest in spring when the colder regions of Northern Europe have snow and sufficient solar radiation to observe the snow-albedo effect. It would be reasonable to expect that NA and Europe would have similar results during this season.
- The paper would benefit from being restructured. It would be clearer if the results focused first on the biogeophysical impacts of forestation in NA and finish by contextualizing these results with the previous work in Europe i.e., section 3 should be just before the conclusions and discussions.
- Section 3 focuses more on comparing the results from NA with Europe. This is good but given the large intermodel variability and the availability of an ensemble for each region, it is recommended that the ensemble for each region is used to improve the robustness of the results in this section.
- It is important to recognize in the conclusions, and perhaps the paper more broadly, that the ensemble size for NA is quite small.
Citation: https://doi.org/10.5194/egusphere-2022-291-RC1 - AC1: 'Reply on RC1', Olivier Asselin, 07 Jul 2022
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RC2: 'Comment on egusphere-2022-291', Anonymous Referee #2, 09 Jun 2022
In this paper, the authors applied three regional climate models to simulate the biophysical climate response to severe (full forest minus grass) forestation in North America and Europe. It is found that the temperature and other physical variables response is largely consistent between North America and Europe by using the same model – CRCM5. The winter warming in high latitudes has been primarily attributed to the snow masking effect of increased tree cover in needleleaf, while the summer cooling in lower latitude has been found to be related to the increased evaporative fraction (i.e., ratio of latent heat to total turbulent heat flux) due to increased broadleaf fraction. The authors also made detailed comparisons across three different models. I believe the idea is not new, but the authors did provide reliable results and conclusions. The conclusion may provide basis for potential forestation over the North America. Below lists my comments.
1. Parameter uncertainty might directly affect the biophysical climate response to forestation across the models. In particular, the authors show that the WRF-NOAH model is lack of snow masking effect and has a quite different minimum stomatal resistance for Needleleaf and Grasses as compared to the CRCM-CLASS model. I’d like to push the authors one more step to at least discuss the fidelity of the stomatal conductance parameter in these models.
2. The minimum stomatal resistance for Needleleaf in WRF-NOAH is only half of that in the CRCM-CLASS. What is the possible true value or range of the Needleleaf stomatal resistance in the observations? It looks like that the low stomatal resistance in WRF-NOAH directly contributes to the increased latent heat fluxes and precipitation in boreal North America during the summertime. Therefore, discussion on the possible true value of the Needleleaf minimum stomatal resistance parameter is necessary as it may make large influence on the biophysical climate effects.
3. The simulations were analyzed over 1986-2015. The climate initial conditions are different among these 30 years. Does this affect the air temperature and rainfall response signal? What is the inter-annual variability in the air temperature and precipitation response to severe forestation?
4. The winter biophysical climate response to severe forestation over North America has been repeatedly shown for CRCM5 in Fig. 2 and Fig. 5, and the same for summer climate response in Fig. 3 and Fig. 8. Is there a way to reduce this redundance?
Citation: https://doi.org/10.5194/egusphere-2022-291-RC2 - AC2: 'Reply on RC2', Olivier Asselin, 07 Jul 2022
Status: closed
-
RC1: 'Comment on egusphere-2022-291', Anonymous Referee #1, 25 May 2022
General Comment
This study uses three regional climate models, albeit two of them are very similar (CRCM5 and CRCM6), to assess the biogeophysical impacts of forestation in North America (NA). The methodology follows the protocol designed in the first phase of the CORDEX flagship pilot study Land Use and Climate Across Scales (LUCAS) and described in Davin et al. (2020). The study also contextualises its results for North America with those already published for Europe, and explores the transferability of results between the two continents. The work is well within the scope of the journal and provides a substantial contribution to the field.
Major Comments
- The title and abstract are a little misleading. This study does not present new results for Europe, nor is Europe its focus. This study focuses primarily on North American and contextualises these results in the framework of the CORDEX LUCAS work for Europe. The results for Europe have been presented previously in Davin et al (2020) and elsewhere, which is correctly referenced throughout the manuscript. In this regard, it is strongly recommended to (a) include North America in the manuscript’s title, and (b) revise some of the sentences in the abstract and introduction to show that the focus is North America.
- It would be beneficial to see a confirmation of the authors hypothesis that the difference between NA and Europe in winter is due to the presence of Evergreen Needleleaf forests and snow cover at lower latitudes in NA compared to Europe.
- It is important to compare the biogeophysical impacts in NA and Europe during spring in addition to the winter. In Europe, the snow albedo effect is strongest in spring when the colder regions of Northern Europe have snow and sufficient solar radiation to observe the snow-albedo effect. It would be reasonable to expect that NA and Europe would have similar results during this season.
- The paper would benefit from being restructured. It would be clearer if the results focused first on the biogeophysical impacts of forestation in NA and finish by contextualizing these results with the previous work in Europe i.e., section 3 should be just before the conclusions and discussions.
- Section 3 focuses more on comparing the results from NA with Europe. This is good but given the large intermodel variability and the availability of an ensemble for each region, it is recommended that the ensemble for each region is used to improve the robustness of the results in this section.
- It is important to recognize in the conclusions, and perhaps the paper more broadly, that the ensemble size for NA is quite small.
Citation: https://doi.org/10.5194/egusphere-2022-291-RC1 - AC1: 'Reply on RC1', Olivier Asselin, 07 Jul 2022
-
RC2: 'Comment on egusphere-2022-291', Anonymous Referee #2, 09 Jun 2022
In this paper, the authors applied three regional climate models to simulate the biophysical climate response to severe (full forest minus grass) forestation in North America and Europe. It is found that the temperature and other physical variables response is largely consistent between North America and Europe by using the same model – CRCM5. The winter warming in high latitudes has been primarily attributed to the snow masking effect of increased tree cover in needleleaf, while the summer cooling in lower latitude has been found to be related to the increased evaporative fraction (i.e., ratio of latent heat to total turbulent heat flux) due to increased broadleaf fraction. The authors also made detailed comparisons across three different models. I believe the idea is not new, but the authors did provide reliable results and conclusions. The conclusion may provide basis for potential forestation over the North America. Below lists my comments.
1. Parameter uncertainty might directly affect the biophysical climate response to forestation across the models. In particular, the authors show that the WRF-NOAH model is lack of snow masking effect and has a quite different minimum stomatal resistance for Needleleaf and Grasses as compared to the CRCM-CLASS model. I’d like to push the authors one more step to at least discuss the fidelity of the stomatal conductance parameter in these models.
2. The minimum stomatal resistance for Needleleaf in WRF-NOAH is only half of that in the CRCM-CLASS. What is the possible true value or range of the Needleleaf stomatal resistance in the observations? It looks like that the low stomatal resistance in WRF-NOAH directly contributes to the increased latent heat fluxes and precipitation in boreal North America during the summertime. Therefore, discussion on the possible true value of the Needleleaf minimum stomatal resistance parameter is necessary as it may make large influence on the biophysical climate effects.
3. The simulations were analyzed over 1986-2015. The climate initial conditions are different among these 30 years. Does this affect the air temperature and rainfall response signal? What is the inter-annual variability in the air temperature and precipitation response to severe forestation?
4. The winter biophysical climate response to severe forestation over North America has been repeatedly shown for CRCM5 in Fig. 2 and Fig. 5, and the same for summer climate response in Fig. 3 and Fig. 8. Is there a way to reduce this redundance?
Citation: https://doi.org/10.5194/egusphere-2022-291-RC2 - AC2: 'Reply on RC2', Olivier Asselin, 07 Jul 2022
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