Local Climate Zone based input for non-building resolving simulation#

Getting a static driver just from a Local Climate Zone and a terrain height map

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In the following, it is described how palm_csd can be used to create a static driver from Local Climate Zone (LCZ) input data for non-building-resolving PALM simulations with the urban parametrization scheme DCEP. Instead of the full data set required otherwise, only the input of an LCZ map and an orography map is needed here. Note that DCEP is currently under revision.

General settings#

With lcz_input, input from LCZ is enabled. Currently, only full instead of the default None is supported. All parameters are derived from LCZ data except orography height. Urban parameters for DCEP are generated when dcep is True. The vertical urban layer heights are set with z_uhl and the urban street directions with udir.

The LCZ can be provided with the lcz input consisting of either one layer with values from 1 to 17 for the 17 LCZ classes or a three-layer file with the RGB values of each LCZ class. The default RGB values are listed below and can be changed as described in the customization section.

An example LCZ data set looks like this:
LCZ map of Berlin, Germany from Demuzere et al. 2022a⁴.

In addition to the LCZ input, palm_csd requires the terrain height.

Customization of LCZ parameters#

This section contains settings to overwrite the default values assigned to each LCZ in the lcz section. The values consist of the parameters assigned by the LCZ classification scheme and the PALM parameters. If it is a LCZ-related value, it is checked if it is within the defined valid range. The setting of a parameter is in the form of type: value. Use the names of classes and parameters as used in the tables in the technical description below. Here is an example:

lcz:
  water:
    b: 255
  open_lowrise:
    building_plan_area_fraction: 0.4
    impervious_plan_area_fraction: 0.2
    aspect_ratio: 0.75

Furthermore, the kind of average used when interpreting the average building height can be set with the height_geometric_mean parameter. If this parameter is set to True, the geometric mean is used; if it is set to False, the arithmetic mean is used.

Technical documentation#

DCEP#

DCEP (Schubert et al. 2012)⁵ is an urban parametrization scheme that calculates the urban radiation and energy fluxes. Buildings are represented by infinitely long street canyons characterized by its building width \(B\), street width \(W\) and its building height distribution with the average \(H\).

Urban impervious surfaces and vegetation are treated as separate tiles with grid cell fractions \(f_\text{urb}\) and \(1-f_\text{urb}\), respectively:

Local Climate Zones#

The Local Climate Zone (LCZ) classification (Stewart and Oke 2012)⁶ consists of the 17 classes.

(Demuzere et al. 2020)²

LCZ classifications are available for many urban areas in the World Urban Database and Access Portal Tool (Ching et al. 2018)¹.

Definition of parameter values#

According to the definition of the LCZ classification, a valid minimum and maximum value of the following parameters are assigned to each LCZ class: mean building-height-to-street-width ratio (aspect ratio) \(\lambda_S\), building surface fraction \(\lambda_B\), impervious (without buildings) and pervious fraction \(\lambda_I\) and \(\lambda_V\), and average roughness element height \(H\). For LCZ1 and LCZ4, a maximum building height was not defined. We follow Demuzere et al. (2022)³ and set these values to 75m.

For the derivation of the required PALM input values, one value within the defined valid range of each parameter is used. This value can be set by the user. The default values are taken from the w2w default values³.

Furthermore, for each LCZ class several PALM properties are assigned: a vegetation type, a water type and a leaf area index for winter and summer. These values can also be adjusted by the user. The vegetation type interrupted_forest is assigned to urban LCZ classes under the assumption of low and high vegetation in these areas. The only additionally required data input is the orography.

The following tables summarize the assigned values for each LCZ class. The tables also show the names of the classes and parameters to be used to customize the values.

class	index		\(\lambda_S\)			\(\lambda_B\)			\(\lambda_I\)			\(\lambda_V\)			\(H\)		r	g	b
		min	default	max	min	default	max	min	default	max	min	default	max	min	default	max
compact_highrise	1	2.00	2.50	None	0.40	0.50	0.60	0.40	0.45	0.60	0.00	0.05	0.10	25.0	avg	75.00	140	0	0
compact_midrise	2	0.75	1.25	2.00	0.40	0.55	0.70	0.30	0.40	0.50	0.00	0.05	0.20	10.0	avg	25.00	209	0	0
compact_lowrise	3	0.75	1.25	1.50	0.40	0.55	0.70	0.20	0.35	0.50	0.00	0.10	0.30	3.0	avg	10.00	255	0	0
open_highrise	4	0.75	1.00	1.25	0.20	0.30	0.40	0.30	0.35	0.40	0.30	0.35	0.40	25.0	avg	75.00	191	77	0
open_midrise	5	0.30	0.50	0.75	0.20	0.30	0.40	0.30	0.40	0.50	0.20	0.30	0.40	10.0	avg	25.00	255	102	0
open_lowrise	6	0.30	0.50	0.75	0.20	0.30	0.40	0.20	0.35	0.50	0.30	0.35	0.60	3.0	avg	10.00	255	153	85
lightweight_lowrise	7	1.00	1.50	2.00	0.60	0.75	0.90	0.00	0.10	0.20	0.00	0.15	0.30	2.0	avg	4.00	250	238	5
large_lowrise	8	0.10	0.20	0.30	0.30	0.40	0.50	0.40	0.45	0.50	0.00	0.15	0.20	3.0	avg	10.00	188	188	188
sparsely_built	9	0.10	0.15	0.25	0.10	0.15	0.20	0.00	0.10	0.20	0.60	0.75	0.80	3.0	avg	10.00	255	204	170
heavy_industry	10	0.20	0.35	0.50	0.20	0.25	0.30	0.20	0.30	0.40	0.40	0.45	0.50	5.0	avg	15.00	85	85	85
dense_trees	11	1.00	2.00	None,	0.00	0.00	0.10	0.00	0.00	0.10	0.90	1.00	1.00	3.0	avg	30.00	0	106	0
scattered_trees	12	0.50	0.65	0.80	0.00	0.00	0.10	0.00	0.00	0.10	0.90	1.00	1.00	3.0	avg	15.00	0	170	0
bush_scrub	13	0.70	0.80	0.90	0.00	0.00	0.10	0.00	0.00	0.10	0.90	1.00	1.00	0.0	1.000	2.00	100	133	37
low_plants	14	0.90	1.00	None,	0.00	0.00	0.10	0.00	0.00	0.10	0.90	1.00	1.00	0.0	0.500	1.00	185	219	121
bare_rock_or_paved	15	0.90	1.00	None,	0.00	0.05	0.10	0.90	0.90	1.00	0.00	0.05	0.10	0.0	0.125	0.25	0	0	0
bare_soil_or_sand	16	0.90	1.00	None,	0.00	0.00	0.10	0.00	0.00	0.10	0.90	1.00	1.00	0.0	0.125	0.25	251	247	174
water	17	0.90	1.00	None,	0.00	0.00	0.10	0.00	0.00	0.10	0.90	1.00	1.00	0.0	0.000	0.00	106	106	205

with

• \(\lambda_S\): aspect_ratio
• \(\lambda_B\): building_plan_area_fraction
• \(\lambda_I\): impervious_plan_area_fraction
• \(\lambda_V\): pervious_plan_area_fraction
• \(H\): height_roughness_elements

The following table shows the default values for the assigned PALM parameters:

class	vegetation_type	water_type	lai_summer	lai_winter
compact_highrise	18	None	1.0	0.1
compact_midrise	18	None	1.0	0.1
compact_lowrise	18	None	1.0	0.1
open_highrise	18	None	2.0	0.5
open_midrise	18	None	2.0	0.5
open_lowrise	18	None	2.0	0.5
lightweight_lowrise	18	None	1.0	0.1
large_lowrise	18	None	0.5	0.1
sparsely_built	18	None	2.0	0.5
heavy_industry	18	None	0.5	0.0
dense_trees	7	None	4.0	0.8
scattered_trees	18	None	2.0	0.5
bush_scrub	16	None	1.0	0.1
low_plants	16	None	1.0	0.1
bare_rock_or_paved	1	None	0.0	0.0
bare_soil_or_sand	1	None	0.0	0.0
water	None	1	None	None

Derivation of DCEP parameters#

The input parameters required by DCEP are derived from the LCZ parameters as follows:

The urban fraction \(f_\text{urb}\) of a grid cell is considered to be the total impervious fraction of a grid cell \(f_\text{urb} = \lambda_B + \lambda_I\). The street width \(W\) is calculated from the average building height and the aspect ratio with \(W = H / \lambda_S\). The building width \(B\) is given by \(B = \lambda_B / \lambda_I \cdot W\).

We follow the approach of Demuzere et al. (2022)³ as implemented in w2w in the calculation of the distribution of the building height: With the probability density function \(f\) of a normal distribution with the mean value \(H\) and a standard deviation \((H_\text{max} - H_\text{min})/4\), the fraction \(p\) of buildings at a height \(h\) is given by $$ p(h) = \int_{h-\Delta H/2}^{h+\Delta H/2} f(x)\, dx \,, $$ with \(\Delta H\) being the layer thickness. Numerically, the integral is directly calculated with the cumulative distribution function of the given normal distribution using scipy⁷. Contrary to Demuzere et al. (2022)³, the user can choose whether the arithmetic or the geometric mean of the building heights is to be used. In the original tool, the arithmetic average is used while the LCZ definition is based on the geometric mean⁶.