Understanding how landform and landcover modulate the spatial and temporal variability of orographic clouds and precipitation

The objective of this project is to investigate whether and how landform and landcover modulate the spatial and temporal variability of orographic clouds and precipitation in a high priority area for biodiversity conservation and human water supply. The central research hypothesis is that evapotranspiration is a critical source of moisture to the atmospheric boundary layer (ABL) either locally and, or remotely via moist transport by diurnal mountain-valley circulations, lowering the cloud base at high elevations during the afternoon, and enhancing thermodynamic instability at locations in the landscape where precipitable water and CAPE (Convective Available Potential Energy) attain collocated night-time maxima. Spatial patterns in the organization of convective initiation are proposed to be explained by the spatial variability of vegetation and soil moisture patterns on altitudinal gradients, and by how this translates into the spatial variability of the diurnal cycle of latent heating fluxes between the land surface and the lower troposphere.


Specifically, the following science questions are being addressed: (1) What is the contribution of evapotranspiration to the diurnal cycle of the energy budget of the lower troposphere in tropical mountainous regions?  How does it vary spatially with elevation and landform (ridges versus valleys, windward versus leeward slopes, foothills versus high peaks)?  (2) How does transversal (lateral) mountain variability in the spatial arrangement of landform and vegetation affect the diurnal cycle of convective activity and precipitation during the monsoon? (3) What is the relationship between the observed multi-scaling behavior of cloud fields from satellite imagery and the dominant spatial scales of convective activity associated with topography and, or land-use/land-cover patterns? (4) How can the current trends of land-use/land-cover change, and in particular deforestation and extension of agricultural activity to the highlands, change the water cycle in tropical mountainous regions?  What are the consequences of these changes for the long-term sustainability of tropical mountain ecosystems and water resources?


Five major activities have been carried out. Hypothesis testing, evaluation and validation of methodologies were conducted for US case-studies when data were not available in the region of study that could be used for this purpose. The methodologies are then transferred to the project's region of study.  

1) Field Observations  -  A network of hydrometeorological towers including above canopy measurements was installed and is being maintained  in the Kospiñata river valley, a tributary  of the Madre De Dios and Madeira rivers in the Amazon basin, in the Central Andes, Peru. The network spans roughly 4,000m on the envelope orography of Manu National Park.

2) Physical Modeling of Land-Atmosphere Interactions - Extensive modeling work with the WRF-ARW model has been carried out in order to use the model at very high resolution (~.2 km) over the very steep terrain of the Andes both at weather and climate time-scales, including ensemble simulations.  In preparation for this work the first simulations of the propagation of a hurricane (tropical storm) after landfall over the SE US and over complex terrain were conducted as a means to develop modeling skills and test and understand the model physics and numerics. For the Andes simulations, specific modeling research was required including addressing boundary layer processes from the representation of forest canopy to the parameterization of aerodynamic roughness, parameterization of convection, and developing physically-based framework to tracks land-atmosphere interactions at sub-second scale to isolate evapotranspiration feedbacks on atmospheric moisture processes from other sources and sinks of atmospheric moisture and energy. Half a million hours of NCAR supercomputer time was used to complete the model simulations, and about 100 Tb of data were generated by the model simulations.

3) Physical-Statistical Modeling of Climate-Landscape Evolution Feedbacks - Development of a statistical-physical model to link modern climate forcing to erosion rates in the Andes;

4) Scaling Analysis of Orographic Convection - Investigation of dynamical physical-statistical downscaling techniques, specifically focusing on the scaling behavior or cloudiness and precipitation under different convection regimes;

5) Diurnal Cycle Dynamics - Characterization of Diurnal Cycle Dynamics focusing on: 1) remote and local controls on atmospheric stability; and 2) the deep convection gap above 3,000 m on the eastern slopes of the Andes.  These studies are conducted using model results from activity (2), satellite data analysis, and nonlinear metrics.


Specific objectives related to each one of the major activities are as follows:

1) Characterize the diurnal, seasonal and  inter-annual variability of orographic precipitation processes on the Eastern Andes slopes that serve as the headwaters of the Amazon  basin;

2) Characterize the diurnal cycle of land-atmosphere interactions from the tropical forest up to the cloud forest in the headwaters of the Amazon basin for the dominant hydrometeorological regimes in the monsoon and dry seasons;

3) Characterize quantitatively the relationship between precipitation and material fluxes from the Eastern Andes to the Amazon foreland;

4) Characterize the dynamic scaling of orographic convection and develop a downscaling framework to enable high spatial resolution climate simulations on the eastern Andes and elsewhere over complex terrain.

5) Explain the dynamical underpinnings of the diurnal cycles of clouds and precipitation in the eastern slopes of the Andes toward elucidating the feedbacks between topography, ecohydrology, and climate.