multiple effects of urban area on reinforcement of ... effects of urban area on reinforcement of...

Multiple Effects of Urban Area on Reinforcement of Precipitation

Tadao Inoue, Ph.DJAMSTEC

JAPAN

t_inoue＠ jamstec.go.jp

2014-08-20Room 520A

No. 58390

Contents

1. Introduction

2. Analysis of radar-based data for precipitation around Tokyo, Japan

3. Numerical Experiment of precipitation in and around large urban area (Tokyo)

Land use of Tokyo is very complex!

©BLUE STYLE COM (Japan)

Urban-A

Urban-B

Introduction

• In recent years, some parts of Tokyo are damaged by local heavy rains. They gave raise to overflow of rivers within the urban area, and not only damaged to properties but also took the lives of people in some cases (Soma et al., 2013).

• Although these local heavy rains are speculated to be caused by existence of urban areas, there is no particular evidence, especially in Tokyo, and mechanisms of them are still unclear.

IntroductionFactors of urban impact to precipitation are as follows:

1. Urban Roughness (Dynamic effect)

2. Radiation Budget (Thermal effect)

3. Thermal Conductivity (Thermal effect)

4. Anthropogenic Heat (Thermal effect)

5. Cloud Condensation Nuclei (CCN effect)

6. Wind Convergence caused by UHI effect

Causes of those impact listed above as follows:• Urban Canopy Layer (1, 2, 3)• Human Activities (4, 5)

IntroductionObservational studies about Tokyo:

1. Fujibe et al. (2009) indicated increasing trend of precipitation at central Tokyo from 118-year data and positive spatial anomaly in Tokyo from afternoon to early evening in warm season (Left panel).

2. Takahashi et al. (2011) shows that there is spatial anomaly of high intensity precipitation (≧ 20 mm h-1 ) in spatial scales less than 10 km (Right panel).

IntroductionNumerical Experiment studies around Tokyo:

• Inamura et al.(2011) implies that changes of wind convergence in leeward of urban area augment precipitation by ensemble experiments using RAMS with many lateral boundaries for many heavy rain cases.

• Souma et al.(2013) conducted unique numerical experiments which set urban areas as (a)UCL+AH, (b)UCL-only, and (c)Water-covered-UCL+AH for a local heavy rain case that killed five people working in drainage pipe.

• Kusaka et al. (2014) implies that (1) increasing of SH in urban area leads to development of PBL and instability, and (2) anomalous low pressure cause convergence of horizontal moisture flux result in an overall increase in precipitation around Tokyo by conducting ensemble experiment of August in eight years with multi reanalysis data.

Another Aspect of Urban Impact

• Urban Heat Island (UHI) is a well known phenomenon and its mechanism is also well understood.

• Urban impact to precipitation is still unclear.

• By the way, is urban impact to cloud formation and maintenance of cloud?

Next, I will introduce my previous research which strongly relates today’s topic!

Clouds over urban area• Cloud Frequency in urban area is higher than that of

rural areas in summer .

• Clouds formed over urban area are very active cumulus clouds, and maintained long-period (more than a few hours). Those clouds seems to be caused by thermals released from urban surface or anthropogenic (SH).

• Increased SH in urban area make PBL higher and clouds form on the top of PBL. Compensating downward flows induced by ascending flow in urban area repress cloud formation in rural area.

NDVI Cloud frequency

• Cloud frequency is high in the urban areas (Low NDVI area) than rural areas in the plain.

• Cloud frequency is highest in the mountain areas and lowest over the water surface.

Inoue and Kimura (2004)

Cross section

Cloud frequency is negatively well correlated with NDVI and their peaks fit well within a shift of about 2 km.

NDVI

Cloud frequency

Urban

Rural

Observed urban clouds (4 Aug. 2003)

Terra/MODIS observed at 10:35 LST

Observed urban clouds (4 Aug. 2003) (Inoue et al. (2004): in Japanese with color photo)

1020 LST

1200 LST

CTRL N00

Comparison between CTRL and No-Urban case (N00)

Inoue and Kimura (2007)

Comparison between CTRL and No-Urban case (N00)

CTRL N00

“Region A” is covered by Sea-brease.

Clo

ud F

ractio

n (

%)

Clo

ud F

ractio

n (

%)

The purpose of the study

• Many states of “urban” are mixed in Tokyo, therefore It is unreasonable to define “urban area” as a whole due to complex land use. When we consider the factors of urban impact to precipitation, we should observe the place from various points of view.

• If strengthening upward flow is assumed as final contribution of urban impact to reinforce and maintain or initiation of precipitation, to find out the “roots” of strengthening upward flaw will connect to understanding of urban impact on precipitation.

• The purpose of the study is to clarify the relationship between places of precipitation generation or enforcement and physical property of those places.

Analysis of radar-based data for precipitation around Tokyo, Japan

Spatial Distribution of Precipitation Frequency

• DATA: "Radar/Raingauge-Analyzed Precipitation(PAP)" ; C-band radar rain gauge adjusted quantitatively by the high density ground-based rain gauge network.

• Period: 2008-2012 (5-year), Apr.-Oct. (Warm season; 7-month)• Horizontal Resolution: 1km x 1km• Time Interval: 30-minite (hourly value)• Target Region: Tokyo metropolitan area• Frequency of Prec.: Num. of count for “Prec. >= x mm h-1” is

normalized by the total Num. of Obs. (x=5, 20)• Number of observation: approximately 50,000• Data processing is conducted by Japan Meteorological Agency(JMA)

and provided by Ministry of Land, Infrastructure, Transport and Tourism(MLIT), Japan.

• Some of original data which are used in the data processing are not disclosed….

Result of RAP analysis

≧5mm h-1 ≧20mm h-1

Period: 2008-2012, Apr.-Oct. (Warm season)

Urban-A

Urban-B

Urban-C

Forest

Result of RAP analysis

≧5mm h-1 ≧20mm h-1

Period: 2008-2012, Apr.-Oct. (Warm season)

Urban-A

Urban-B

Urban-C

Forest

Solid lines indicate "Railroad"

Tokyo Bay

Tokyo Station

a) Land useb) NDVI

RAP: c) ≧5mm h-1

d) ≧20mm h-1

a) b)

c) d)

Imperfectness of the data:• The main purpose of the data is near-real-time

monitoring of precipitation intensity to alert before a flood disaster occurs.

• If an estimated precipitation intensity of a grid which contains a ground-based rain gauge is lower than that of rain gauge, the value of the grid is replaced by the rain gauge value.

• Values of rain gauge grids is sometimes comparatively higher than surrounding grids. Adjacent grids are also strongly affected by distance-weighted interpolation.

• As a result, the frequency of the grids are relatively higher as if some noise are added to the grids.

Problem of Statistic Analysis for RAP data

A grid of RAPrain gauge: 5mm h-1

Radar

If estimated precipitation intensity of a grid which contains a ground-based rain gauge is lower than that of rain gauge, the value of the grid is replaced by the rain gauge value. Because the main purpose of the data is near-real-time monitoring precipitation intensity to alert before a flood disaster.

3mm h-1 3mm h-1

Prec. intensity estimated from radar echo

3mm h-1 5mm h-1Prec. intensity of RAP data

= >=

<

Tokyo Bay

Tokyo Station

a) Land use

RAP: b) ≧1mm h-1

c) ≧5mm h-1

d) ≧20mm h-1

a) b)

c) d)

Noisy…

Summary of RAP analysis

• Spatial distribution of precipitation frequency in warm season is not uniform. This result supports Takahashi et al. (2011). Moreover, detailed spatial anomaly is found and some of higher and lower area correspond to land use.

• Higher frequency of the grid which includes “Tokyo” observation station confirms Fujibe et al. (2009), although imperfection of the data exists and some noise resulting from data processing algorithm is added to the grid.

Higher Density Rain gaugesBlue and red symbols indicate locations of observation used in RAP and in the middle of collecting from the 23 special wards of Tokyo and other local governments, respectively.

New(?) Aspects of Urban Impact to Precipitation

• Effects of combinations of factors are different in a time zone of an event, or a day of week, or weather prior to an event, or a type of precipitation (move into urban area or generate in urban area).

• Early in the morning, urban canopy layer (building site) insensitive to solar radiation due to its thermal inertia. Number of cars is not so large. AH released form buildings is also little. Then, urban area may work week for urban impact to precipitation.

• For a day of relatively lower radiation, AH will be more important than a sunny day.

• Therefore, timing of a event must be considered when we think about urban impact to precipitation.

Numerical Experiment of precipitation in and around large

urban area (Tokyo)

Setting of WRF• Model: ARW-WRF Ver. 3.5.1• The center-point of the coarse domain: 35N, 138E• D1: 112 x 91, D2: 125 x 97; D3: 145 x 118; D4: 241 x 181• Horizontal Resolution: 24km, 6km, 2km, 0.5km• Vertical Resolution: 40-layer (Thickness of the lowest layer is 40-m)• Two way nesting• Physics:

Microphysics=WSM6; Longwave Radiation=RRTMG scheme(new Rapid Radiative Transfer Model); Shortwave Radiation=RRTMG shortwave;Surface Layer=MM5 similarity;Land Surface=Noah Land Surface Model;Planetary Boundary layer=Mellor-Yamada Nakanishi and Niino Level 2.5 PBL;Urban Surface=Urban canopy model (Single-layer);Cumulus Parameterization(d1, d2)=Kain-Fritsch scheme

• Boundary condition: ERA-Interim(0.7 degrees spatial resolution, and 37 atmospheric levels. 6hr interval)

• Map Projection: Lambert Conformal

Setting of WRF domains

Domain 1 Domain 2

Domain 3

Domain 4

Setting of urban areas in WRF

Urban-A

Urban-B

Urban-C

Forest

Urban-A Urban-B Urban-CUrban-BUrban-C

Setting of urban areas in WRFLand use categories

max-AH Ave-height Thermal-conductivity

Urban-A Buildings and factories

300W m-2 20m 2.0J m-1 s-1 K-1

Urban-B High-density residential

200W m-2 10m 1.2J m-1 s-1 K-1

Urban-C Low-density residential

20W m-2 5m 0.67J m-1 s-1 K-1

Setting of Numerical ExperimentName of Experiment Anthropogenic Heat Urban Canopy

Exp-1 (Control-run) ○ ○

Exp-2 ○ △

Exp-3 × ○

△ (Urban Canopy in Exp-2): Canopy in All urban categories is set as Urban-C type

Exp-1

+ Anthropogenic Heat + Anthropogenic Heat

Exp-2

No Anthropogenic Heat

Exp-3

Setting of Numerical Experiment

Case-0: from 2010-07-10_09LST(00z) to 2010-07-26_09LST(00z)For temperature sensitivity check.Almost clear and very hot days with some local thunder storm.

Case-1: from 2009-08-07_00Z(09LT) to 2009-08-07_12Z(21LT)Rain-band moves from west.

Case-2: from 2009-06-16_00Z(09LT) to 2009-06-16_12Z(21LT)Rain-band moves from west.

Ensemble-like experiments using WRF-Four Dimensional Data Assimilation(FDDA):• Inner grid nudging; Adapt Domain-1; uv for free atmosphere

(Case-1 & 2)• 1, 2, 3-hr from Start; nudging inverse time scale (0.0003 or

0.0001) = 6-ensemble

* Precipitation initiation case is difficult to reproduce in a model, so moving rain-band case were selected.

Comparison of Temperature (2m) between observation and WRF:2010/07/10_09LST-2010/07/26_09LST (Case-0)

Tokyo: Ur-A

Nerima: Ur-B

Exp-1 Exp-2 Exp-3

X:Obs.

Y: W

RF

Case-1Time Series of SH and Precipitation

2009-08-07

0

1

2

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6

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W m

-2Sensible Heat Flux and Precipitaion amount (Area mean)

15AFBem 15AFFem

15NABem 15AFBem

15AFFem 15NABem

■ Exp-1■ Exp-2■ Exp-3

Hourly rain at 2009-08-07_10:00Z(in WRF; 19:00LST)

Exp-1

Exp-2 Exp-3

RAP(-0.5hr)

20mm h-1 20mm h-1

20mm h-1 20mm h-1

Hourly u,v,w 900hPa at 2009-08-07_10:00Z(in WRF; 19:00LST)

Exp-1

Exp-2 Exp-3

20mm h-1 0.8m s-1

0.8m s-1 0.8m s-1

Exp-1


Exp-1

Exp-2 Exp-3

RAP

20mm h-1 20mm h-1

20mm h-1 20mm h-1

Case-2Time Series of SH and Precipitation

2009-06-16

0

0.5

1

1.5

2

2.5

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3.5

4

4.5

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W m

-2

Sensible Heat Flux and Precipitation amount (Area mean)

17AFBem 17AFFem

17NABem 17AFBem

17AFFem 17NABem

■ Exp-1■ Exp-2■ Exp-3


Exp-1

Exp-2 Exp-3

RAP(+2.5hr)

20mm h-1 20mm h-1

20mm h-1 20mm h-1


Exp-1

Exp-2 Exp-3

RAP

20mm h-1 20mm h-1

20mm h-1 20mm h-1

Hourly u,v,w 900hPa at 2009-06-16_10:00Z(in WRF; 19:00LST)

Exp-1

Exp-2 Exp-3

20mm h-1 1.2m s-1

1.2m s-1 1.2m s-1

Exp-1


Exp-1

Exp-2 Exp-3

RAP

20mm h-1 20mm h-1

20mm h-1 20mm h-1

Summary

• Numerical experiments were conducted to detect urban impact to precipitation with three setup of urban areas above.

• In the period of continuous sunny days, surface temperature of Exp-1 is most closely match to observation.

• Numerical experiment for 2-case which rain-bands move from western side were conducted. In Exp-1&2 that includes AH, upward flow was enforced and precipitation intensity was also increased.

Exp-1

+ Anthropogenic Heat + Anthropogenic Heat

Exp-2

No Anthropogenic Heat

Exp-3

Thank you for your attention!

Acknowledgment:

This research is funded by

"Research Program on Climate Change Adaptation（RECCA）"

of MEXT, Japan

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